It is called "Essential". There are no errors in the browser console. I use no other non core plugins. Its on every page - but the hitch has only shown up on 2 of 4 tested systems. Both systems with the problem used firefox with resolutions higher than full hd.
{
"moodle_version": "2017051501.03",
"theme_version": "2017040302",
"alert1text": "",
"alert1title": "",
"alert1type": "error",
"alert2text": "",
"alert2title": "",
"alert2type": "info",
"alert3text": "",
"alert3title": "",
"alert3type": "info",
"alternativethemecolor1": "#a430d1",
"alternativethemecolor2": "#d15430",
"alternativethemecolor3": "#5dd130",
"alternativethemecolor4": "#006b94",
"alternativethemedefaultbuttonbackgroundcolour1": "#30add1",
"alternativethemedefaultbuttonbackgroundcolour2": "#30add1",
"alternativethemedefaultbuttonbackgroundcolour3": "#30add1",
"alternativethemedefaultbuttonbackgroundcolour4": "#30add1",
"alternativethemedefaultbuttontextcolour1": "#ffffff",
"alternativethemedefaultbuttontextcolour2": "#ffffff",
"alternativethemedefaultbuttontextcolour3": "#ffffff",
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"alternativethemedefaultbuttontexthovercolour1": "#ffffff",
"alternativethemedefaultbuttontexthovercolour2": "#ffffff",
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"alternativethemedefaultbuttontexthovercolour4": "#ffffff",
"alternativethemedefbuttonbackgroundhvrcolour1": "#3ad4ff",
"alternativethemedefbuttonbackgroundhvrcolour2": "#3ad4ff",
"alternativethemedefbuttonbackgroundhvrcolour3": "#3ad4ff",
"alternativethemedefbuttonbackgroundhvrcolour4": "#3ad4ff",
"alternativethemefooterblockbackgroundcolour1": "#cccccc",
"alternativethemefooterblockbackgroundcolour2": "#cccccc",
"alternativethemefooterblockbackgroundcolour3": "#cccccc",
"alternativethemefooterblockbackgroundcolour4": "#cccccc",
"alternativethemefooterblockhovercolour1": "#555555",
"alternativethemefooterblockhovercolour2": "#555555",
"alternativethemefooterblockhovercolour3": "#555555",
"alternativethemefooterblockhovercolour4": "#555555",
"alternativethemefooterblocktextcolour1": "#000000",
"alternativethemefooterblocktextcolour2": "#000000",
"alternativethemefooterblocktextcolour3": "#000000",
"alternativethemefooterblocktextcolour4": "#000000",
"alternativethemefooterblockurlcolour1": "#000000",
"alternativethemefooterblockurlcolour2": "#000000",
"alternativethemefooterblockurlcolour3": "#000000",
"alternativethemefooterblockurlcolour4": "#000000",
"alternativethemefootercolor1": "#30add1",
"alternativethemefootercolor2": "#30add1",
"alternativethemefootercolor3": "#30add1",
"alternativethemefootercolor4": "#30add1",
"alternativethemefooterheadingcolor1": "#cccccc",
"alternativethemefooterheadingcolor2": "#cccccc",
"alternativethemefooterheadingcolor3": "#cccccc",
"alternativethemefooterheadingcolor4": "#cccccc",
"alternativethemefooterhovercolor1": "#bbbbbb",
"alternativethemefooterhovercolor2": "#bbbbbb",
"alternativethemefooterhovercolor3": "#bbbbbb",
"alternativethemefooterhovercolor4": "#bbbbbb",
"alternativethemefootersepcolor1": "#313131",
"alternativethemefootersepcolor2": "#313131",
"alternativethemefootersepcolor3": "#313131",
"alternativethemefootersepcolor4": "#313131",
"alternativethemefootertextcolor1": "#ffffff",
"alternativethemefootertextcolor2": "#ffffff",
"alternativethemefootertextcolor3": "#ffffff",
"alternativethemefootertextcolor4": "#ffffff",
"alternativethemefooterurlcolor1": "#cccccc",
"alternativethemefooterurlcolor2": "#cccccc",
"alternativethemefooterurlcolor3": "#cccccc",
"alternativethemefooterurlcolor4": "#cccccc",
"alternativethemehovercolor1": "#9929c4",
"alternativethemehovercolor2": "#c44c29",
"alternativethemehovercolor3": "#53c429",
"alternativethemehovercolor4": "#4090af",
"alternativethemeiconcolor1": "#a430d1",
"alternativethemeiconcolor2": "#d15430",
"alternativethemeiconcolor3": "#5dd130",
"alternativethemeiconcolor4": "#006b94",
"alternativethememycoursesorderenrolbackcolour1": "#a3ebff",
"alternativethememycoursesorderenrolbackcolour2": "#a3ebff",
"alternativethememycoursesorderenrolbackcolour3": "#a3ebff",
"alternativethememycoursesorderenrolbackcolour4": "#a3ebff",
"alternativethemename1": "Alternative colours 1",
"alternativethemename2": "Alternative colours 2",
"alternativethemename3": "Alternative colours 3",
"alternativethemename4": "Alternative colours 4",
"alternativethemenavcolor1": "#ffffff",
"alternativethemenavcolor2": "#ffffff",
"alternativethemenavcolor3": "#ffffff",
"alternativethemenavcolor4": "#ffffff",
"alternativethemeslidebuttoncolor1": "#a430d1",
"alternativethemeslidebuttoncolor2": "#d15430",
"alternativethemeslidebuttoncolor3": "#5dd130",
"alternativethemeslidebuttoncolor4": "#006b94",
"alternativethemeslidebuttonhovercolor1": "#9929c4",
"alternativethemeslidebuttonhovercolor2": "#c44c29",
"alternativethemeslidebuttonhovercolor3": "#53c429",
"alternativethemeslidebuttonhovercolor4": "#4090af",
"alternativethemeslidecaptionbackgroundcolor1": "#a430d1",
"alternativethemeslidecaptionbackgroundcolor2": "#d15430",
"alternativethemeslidecaptionbackgroundcolor3": "#5dd130",
"alternativethemeslidecaptionbackgroundcolor4": "#006b94",
"alternativethemeslidecaptiontextcolor1": "#ffffff",
"alternativethemeslidecaptiontextcolor2": "#ffffff",
"alternativethemeslidecaptiontextcolor3": "#ffffff",
"alternativethemeslidecaptiontextcolor4": "#ffffff",
"alternativethemestripebackgroundcolour1": "#c1009f",
"alternativethemestripebackgroundcolour2": "#bc2800",
"alternativethemestripebackgroundcolour3": "#b4b2fd",
"alternativethemestripebackgroundcolour4": "#0336b4",
"alternativethemestripetextcolour1": "#bdfdb7",
"alternativethemestripetextcolour2": "#c3fdd0",
"alternativethemestripetextcolour3": "#9f5bfb",
"alternativethemestripetextcolour4": "#ff1ebd",
"alternativethemestripeurlcolour1": "#bef500",
"alternativethemestripeurlcolour2": "#30af67",
"alternativethemestripeurlcolour3": "#ffe9a6",
"alternativethemestripeurlcolour4": "#ffab00",
"alternativethemetextcolor1": "#a430d1",
"alternativethemetextcolor2": "#d15430",
"alternativethemetextcolor3": "#5dd130",
"alternativethemetextcolor4": "#006b94",
"alternativethemeurlcolor1": "#a430d1",
"alternativethemeurlcolor2": "#d15430",
"alternativethemeurlcolor3": "#5dd130",
"alternativethemeurlcolor4": "#006b94",
"analytics": "piwik",
"analyticscleanurl": "",
"analyticsenabled": "",
"analyticsimagetrack": "",
"analyticssiteid": "1",
"analyticssiteurl": "",
"analyticstrackadmin": "",
"analyticsuseuserid": "",
"android": "",
"breadcrumbstyle": "4",
"categoryct12image": "",
"categoryct15image": "",
"categoryct17image": "",
"categoryct18image": "",
"categoryct19image": "",
"categoryct1image": "",
"categoryct20image": "",
"categoryct23image": "",
"categoryct24image": "",
"categoryct25image": "",
"categoryct27image": "",
"categoryct28image": "",
"categoryct2image": "",
"categoryct30image": "",
"categoryct32image": "",
"categoryct34image": "",
"categoryct36image": "",
"categoryct37image": "",
"categoryct4image": "",
"categoryct5image": "",
"categoryct6image": "",
"categorycti12height": "200",
"categorycti12textbackgroundcolour": "#ffffff",
"categorycti12textbackgroundopactity": "0.8",
"categorycti12textcolour": "#000000",
"categorycti15height": "200",
"categorycti15textbackgroundcolour": "#ffffff",
"categorycti15textbackgroundopactity": "0.8",
"categorycti15textcolour": "#000000",
"categorycti17height": "200",
"categorycti17textbackgroundcolour": "#ffffff",
"categorycti17textbackgroundopactity": "0.8",
"categorycti17textcolour": "#000000",
"categorycti18height": "200",
"categorycti18textbackgroundcolour": "#ffffff",
"categorycti18textbackgroundopactity": "0.8",
"categorycti18textcolour": "#000000",
"categorycti19height": "200",
"categorycti19textbackgroundcolour": "#ffffff",
"categorycti19textbackgroundopactity": "0.8",
"categorycti19textcolour": "#000000",
"categorycti1height": "200",
"categorycti1textbackgroundcolour": "#ffffff",
"categorycti1textbackgroundopactity": "0.8",
"categorycti1textcolour": "#000000",
"categorycti20height": "200",
"categorycti20textbackgroundcolour": "#ffffff",
"categorycti20textbackgroundopactity": "0.8",
"categorycti20textcolour": "#000000",
"categorycti23height": "200",
"categorycti23textbackgroundcolour": "#ffffff",
"categorycti23textbackgroundopactity": "0.8",
"categorycti23textcolour": "#000000",
"categorycti24height": "200",
"categorycti24textbackgroundcolour": "#ffffff",
"categorycti24textbackgroundopactity": "0.8",
"categorycti24textcolour": "#000000",
"categorycti25height": "200",
"categorycti25textbackgroundcolour": "#ffffff",
"categorycti25textbackgroundopactity": "0.8",
"categorycti25textcolour": "#000000",
"categorycti27height": "200",
"categorycti27textbackgroundcolour": "#ffffff",
"categorycti27textbackgroundopactity": "0.8",
"categorycti27textcolour": "#000000",
"categorycti28height": "200",
"categorycti28textbackgroundcolour": "#ffffff",
"categorycti28textbackgroundopactity": "0.8",
"categorycti28textcolour": "#000000",
"categorycti2height": "200",
"categorycti2textbackgroundcolour": "#ffffff",
"categorycti2textbackgroundopactity": "0.8",
"categorycti2textcolour": "#000000",
"categorycti30height": "200",
"categorycti30textbackgroundcolour": "#ffffff",
"categorycti30textbackgroundopactity": "0.8",
"categorycti30textcolour": "#000000",
"categorycti32height": "200",
"categorycti32textbackgroundcolour": "#ffffff",
"categorycti32textbackgroundopactity": "0.8",
"categorycti32textcolour": "#000000",
"categorycti34height": "200",
"categorycti34textbackgroundcolour": "#ffffff",
"categorycti34textbackgroundopactity": "0.8",
"categorycti34textcolour": "#000000",
"categorycti36height": "200",
"categorycti36textbackgroundcolour": "#ffffff",
"categorycti36textbackgroundopactity": "0.8",
"categorycti36textcolour": "#000000",
"categorycti37height": "200",
"categorycti37textbackgroundcolour": "#ffffff",
"categorycti37textbackgroundopactity": "0.8",
"categorycti37textcolour": "#000000",
"categorycti4height": "200",
"categorycti4textbackgroundcolour": "#ffffff",
"categorycti4textbackgroundopactity": "0.8",
"categorycti4textcolour": "#000000",
"categorycti5height": "200",
"categorycti5textbackgroundcolour": "#ffffff",
"categorycti5textbackgroundopactity": "0.8",
"categorycti5textcolour": "#000000",
"categorycti6height": "200",
"categorycti6textbackgroundcolour": "#ffffff",
"categorycti6textbackgroundopactity": "0.8",
"categorycti6textcolour": "#000000",
"categoryctimageurl1": "",
"categoryctimageurl12": "",
"categoryctimageurl15": "",
"categoryctimageurl17": "",
"categoryctimageurl18": "",
"categoryctimageurl19": "",
"categoryctimageurl2": "",
"categoryctimageurl20": "",
"categoryctimageurl23": "",
"categoryctimageurl24": "",
"categoryctimageurl25": "",
"categoryctimageurl27": "",
"categoryctimageurl28": "",
"categoryctimageurl30": "",
"categoryctimageurl32": "",
"categoryctimageurl34": "",
"categoryctimageurl36": "",
"categoryctimageurl37": "",
"categoryctimageurl4": "",
"categoryctimageurl5": "",
"categoryctimageurl6": "",
"categoryicon1": "",
"categoryicon12": "",
"categoryicon15": "",
"categoryicon17": "",
"categoryicon18": "",
"categoryicon19": "",
"categoryicon2": "",
"categoryicon20": "",
"categoryicon23": "",
"categoryicon24": "",
"categoryicon25": "",
"categoryicon27": "",
"categoryicon28": "",
"categoryicon30": "",
"categoryicon32": "",
"categoryicon34": "",
"categoryicon36": "",
"categoryicon37": "",
"categoryicon4": "",
"categoryicon5": "",
"categoryicon6": "",
"categoryincoursebreadcrumbfeature": "1",
"copyright": "Hochschule Düsseldorf - Fachbereich Medien",
"coursecontentsearch": "1",
"courselistteachericon": "graduation-cap",
"ctioverrideheight": "200",
"ctioverridetextbackgroundcolour": "#c51230",
"ctioverridetextbackgroundopacity": "0.8",
"ctioverridetextcolour": "#ffffff",
"customcss": "h1 {\r\n font-size: 20px;\r\n}\r\n\r\nh2 {\r\n font-size: 18px;\r\n}\r\n\r\nh3 {\r\n font-size: 16px;\r\n}\r\n\r\nh4 {\r\n font-size: 14px;\r\n}",
"customscrollbars": "1",
"defaultcategoryicon": "folder-open",
"displayeditingmenu": "0",
"displayhiddenmycourses": "1",
"displaymycourses": "1",
"dropdownmenumaxheight": "384",
"dropdownmenuscroll": "",
"enable1alert": "",
"enable2alert": "",
"enable3alert": "",
"enablealternativethemecolors1": "",
"enablealternativethemecolors2": "",
"enablealternativethemecolors3": "",
"enablealternativethemecolors4": "",
"enablecategorycti": "0",
"enablecategoryctics": "0",
"enablecategoryicon": "0",
"enablecustomcategoryicon": "0",
"facebook": "",
"favicon": "/favicon-2.ico",
"fitvids": "1",
"flatnavigation": "1",
"flickr": "",
"floatingsubmitbuttons": "1",
"fontcharacterset": "",
"fontnamebody": "Helvetica",
"fontnameheading": "Helvetica",
"fontselect": "1",
"footerblockbackgroundcolour": "#cccccc",
"footerblockhovercolour": "#555555",
"footerblocktextcolour": "#000000",
"footerblockurlcolour": "#000000",
"footercolor": "#345C83",
"footerheadingcolor": "#cccccc",
"footerhovercolor": "#bbbbbb",
"footersepcolor": "#313131",
"footertextcolor": "#ffffff",
"footerurlcolor": "#cccccc",
"footnote": "<p><span style=\"text-align: center;\"><a href=\"http://moodle.medien.hs-duesseldorf.de/customsites/datenschutz.html\">Datenschutz<\/a> - <a href=\"http://moodle.medien.hs-duesseldorf.de/customsites/impressum.html\">Impressum<\/a><\/span><\/p>",
"fppagetopblocks": "3",
"fppagetopblocksperrow": "3",
"frontcontentarea": "",
"frontpageblocks": "1",
"frontpagehomeblocksperrow": "3",
"frontpagemiddleblocks": "0",
"googleplus": "",
"haveheaderblock": "1",
"headerbackground": "/grau1-3.gif",
"headerbackgroundstyle": "tiled",
"headerblocksperrow": "4",
"headertextcolor": "#F5FEF6",
"headertitle": "0",
"helplink": "",
"helplinktype": "0",
"hidedefaulteditingbutton": "0",
"hideonphone": "1",
"hideontablet": "1",
"instagram": "",
"ios": "",
"ipadicon": "",
"ipadretinaicon": "",
"iphoneicon": "",
"iphoneretinaicon": "",
"layout": "1",
"linkedin": "",
"loginbackground": "",
"loginbackgroundopacity": "0.8",
"loginbackgroundstyle": "cover",
"logo": "/HSD-FB5-moodle-2.jpg",
"logodesktopwidth": "100",
"logoheight": "150px",
"logomobilewidth": "10",
"logowidth": "1200px",
"marketing1": "",
"marketing1buttontext": "",
"marketing1buttonurl": "",
"marketing1content": "",
"marketing1icon": "star",
"marketing1image": "",
"marketing1target": "_blank",
"marketing2": "",
"marketing2buttontext": "",
"marketing2buttonurl": "",
"marketing2content": "",
"marketing2icon": "star",
"marketing2image": "",
"marketing2target": "_blank",
"marketing3": "",
"marketing3buttontext": "",
"marketing3buttonurl": "",
"marketing3content": "",
"marketing3icon": "star",
"marketing3image": "",
"marketing3target": "_blank",
"marketingheight": "100",
"marketingimageheight": "100",
"mycoursescatsubmenu": "",
"mycoursesmax": "0",
"mycoursesorder": "1",
"mycoursesorderenrolbackcolour": "#a3ebff",
"mycoursesorderidorder": "1",
"mycoursetitle": "course",
"navbartitle": "2",
"numberofslides": "4",
"oldnavbar": "1",
"pagebackground": "/grau1-2.gif",
"pagebackgroundstyle": "fixed",
"pagebottomblocksperrow": "4",
"pagetopblocks": "1",
"pagetopblocksperrow": "1",
"pagewidth": "1200",
"perfinfo": "min",
"pinterest": "",
"returntosectionfeature": "1",
"returntosectiontextlimitfeature": "15",
"siteicon": "laptop",
"skype": "",
"slide1": "",
"slide1caption": "<p>Campus Derendorf - Regie Tonstudio<\/p>",
"slide1image": "/613-Regie-Ton-Panorama-2.JPG",
"slide1target": "_self",
"slide1url": "",
"slide2": "",
"slide2caption": "<p>Campus Derendorf - Eingangsbereich Gebäude 4<\/p>",
"slide2image": "/IMG_7652-2.JPG",
"slide2target": "_self",
"slide2url": "",
"slide3": "",
"slide3caption": "<p>Campus Derendorf - Gebäude 4<\/p>",
"slide3image": "/IMG_8742-2.JPG",
"slide3target": "_self",
"slide3url": "",
"slide4": "",
"slide4caption": "<p>Campus Derendorf - Seminarraum FB Medien<br><\/p>",
"slide4image": "/HSD-OG1-9-Hörsaal,ansteigend-151103_17h25_01-2.jpg",
"slide4target": "_self",
"slide4url": "",
"slidebuttoncolor": "#143C63",
"slidebuttonhovercolor": "#217a94",
"slidecaptionbackgroundcolor": "#143C63",
"slidecaptioncentred": "1",
"slidecaptionoptions": "2",
"slidecaptiontextcolor": "#ffffff",
"slideinterval": "5000",
"themecolor": "#143C63",
"themedefaultbuttonbackgroundcolour": "#143C63",
"themedefaultbuttonbackgroundhovercolour": "#FFFEFF",
"themedefaultbuttontextcolour": "#ffffff",
"themedefaultbuttontexthovercolour": "#B20300",
"themehovercolor": "#143C63",
"themeiconcolor": "#555555",
"themenavcolor": "#ffffff",
"themestripebackgroundcolour": "#ff9a34",
"themestripetextcolour": "#ffffff",
"themestripeurlcolour": "#25849f",
"themetextcolor": "#000000",
"themeurlcolor": "#B20300",
"togglefrontcontent": "0",
"togglemarketing": "0",
"toggleslideshow": "0",
"twitter": "",
"userimageborderradius": "90",
"usermenuuserimageborderradius": "4",
"usesiteicon": "1",
"vk": "",
"website": "",
"windows": "",
"winphone": "",
"youtube": ""
}
I will update the plugin as recommended to 3.3.1.0 and check if the bug is still there.