Moodle in English: Save and Show Next freezes on 2nd student

Save and Show Next freezes on 2nd student

by Matt Long - Tuesday, September 22, 2020, 10:54 PM

Hi,

We've been experiencing an unusual problem with grading assignments. When an instructor clicks the "Save and Show Next" button after adding comments and grading the 1st student's assignment, the button works, the grade is saved, and the next student is displayed. However, if they then click "Save and Show Next" again after grading the 2nd student's work, a "Saving changes" message with a spinning circle shows up and the program freezes (the circle keeps spinning indefinitely). I've attached a screenshot of what it looks like. At that point, they have to either close out the window or click the Back button in their browser, either of which will cause the instructor's comments and grade for that student to be lost.

They can then go back to the 2nd student's assignment, click Save and Show Next, and it will work, but the program will freeze again when they click Save and Show Next on the 3rd student's assignment. So the button only works for one student at a time and freezes on the next one.

As far as I can tell, the problem surfaced after we patched our Linux servers last month. We use Centos 7 with Webmin, and we updated the servers through the Webmin interface. However, I'm having trouble figuring out how that process could have caused this issue. Possibly an update to PHP? We're using PHP 7.2.24 running in FCGI, and Zend OpCache is enabled. The resource limits (max input time, etc.) are all set fairly high.

I also thought it could be the PDF annotation with unoconv and LibreOffice since those were likely also updated, but the same error happens even if PDF Annotation is disabled for the assignment.

We are using Moodle 3.5.9+ (Build: 20191122). I attempted to upgrade to 3.9 last month, but unfortunately it broke our theme (Adaptable) when we tried the upgrade on a test server. Hopefully we'll be able to do that after this term, but in the meantime, it would be really helpful for our faculty if we could figure out why the grading screen keeps freezing.

EDIT: I've found another glitch on the 2nd student's screen. The "Change Users" section in the top right doesn't work at all (left and right arrows do nothing and it won't change if you select a student from the dropdown). Also, the dropdown doesn't display the correct number of students even though no filters are applied. So somehow this 2nd student's grade screen is already glitching before the instructor clicks "Save and Show Next." In fact, they don't even have to click "Save and Show Next" on the 2nd student. Just clicking Save Changes will also freeze the screen.

I don't know if anyone else has run into a similar issue, but thanks in advance for any help or advice!

Matt

Re: Save and Show Next freezes on 2nd student

by Matt Long - Wednesday, September 23, 2020, 5:49 AM

We figured this one out. I noticed an unusual error in the Javascript console that referenced "qtype_ordering" when the glitch was happening. I then checked our IT helpdesk tickets, and there had been a request recently from a professor for us to add this question type plugin: https://moodle.org/plugins/qtype_ordering. Once I removed the plugin and cleared out all the caches, the problem resolved.

It looks like a related Javascript issue has already been reported on the plugin page, and I'll report this problem as well.

Matt

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Re: Save and Show Next freezes on 2nd student

by Tim Hunt - Wednesday, September 23, 2020, 3:41 PM

So, the error was; DevTools failed to load SourceMap: Could not parse content for drag_reorder.min.js.map: Unexpected token d in JSON at position 0.

I am a bit suprised if that is the cause, because something that caused a problem for the browser developer tools is unlikely to be the real problem. However, it is probably related to what is really going on.

I think the key thing is, you are using Moodle 3.5, which is quite old. And, the way JavaScript works in Moodle keeps changing as time marches on. So, the JS in the ordering plugin, which was probably compiled with Moodle 3.8+, won't work there.

Still, it is very odd that an error related to one question type (which is normally only used in the quiz) could affect the assignment activity.

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Re: Save and Show Next freezes on 2nd student

by Matt Long - Wednesday, September 23, 2020, 10:56 PM

Hi Tim,
Right, so that was the console message that we saw on all the pages of our site when the plugin was installed. The actual error message after the grading screen glitched was "Uncaught TypeError: Cannot read property 'body' of null." There were several lines after it, so I've included a screenshot.

I was also very surprised that it was affecting all of our pages and not just those within the quiz module. The other person who had a similar problem thought it might be an interaction with the Boost theme and themes that used it as a parent (I'm guessing ours does).

We're really hoping to upgrade to 3.9 soon. It looks like the theme we're using now has a compatible version that was just released in the last few days. Our school has a policy of trying to use LTS versions of software as much as possible for stability reasons.

Matt

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Re: Save and Show Next freezes on 2nd student

by Tim Hunt - Thursday, September 24, 2020, 3:54 PM

Right, it will be that "Uncaught TypeError: Cannot read property 'body' of null." that is what is breaking everything. I think this shows up an interesting flaw in Moodle JavaScript handling. I raise this with the some of the deveopers who konw about these things.

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Re: Save and Show Next freezes on 2nd student

by Matt Long - Thursday, September 24, 2020, 10:29 PM

Hi Tim,
Thanks for looking into this. That would be very interesting to find out, especially because I've just found out that the problem isn't actually resolved.

When I first tested the assignment grading problem and got the error, I was using Google Chrome. That's when I noticed the Javascript warning about the question type plugin. However, when I actually removed the plugin and tested again, I was on a different computer and was using Mozilla Firefox, and the assignment grading was working correctly. So it was a classic "correlation does not imply causation" mistake on my part.

In fact, our assignment grading is still not working in Google Chrome or Chromium-based browsers like MS Edge. It works fine in Mozilla Firefox. I'm assuming this has to do with the different way the browsers handle Javascript. Perhaps there was even a change to Chromium in the past few months that might have triggered this? It wasn't a problem for our summer term courses, and some of those instructors are teaching the same course this Fall and now having the problem. The only changes I can think of on our side since the summer term were the addition of the question type plugin and our standard server updates in Linux.

Anyway, for now, I can at least tell our instructors that they can use Firefox when grading assignments to avoid the error. I'll also make a note of this on the question type plugin page so they know that it wasn't their plugin causing the issue.

If you or someone from Moodle would like access to our site to troubleshoot this further, just let me know.

Hopefully this isn't affecting newer versions of Moodle. I'm assuming it's not since there aren't other reports in these forums. Of course, it's also possible that we have some other plugin or add-on that is now incompatible with Chromium, but I'm not seeing anything in the JS error message that would help us isolate that. It's not ideal for us to require Firefox for assignment grading as most of our instructors use Chrome or Safari (which I haven't tested yet as I don't have a Mac on hand), but it should get us through until we can update to 3.9 after the Fall term.

Matt

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Re: Save and Show Next freezes on 2nd student

by Dillon Esterhuizen - Thursday, October 8, 2020, 12:16 AM

Hi Matt

I've encountered the same issue as you on the same Moodle version but the Javascript error I see is this:

tiny_mce_src.js:10732 Uncaught TypeError: Cannot read property 'body' of null
at NodeList. (tiny_mce_src.js:10732)
at each (tiny_mce_src.js:151)
at Object.serialize (tiny_mce_src.js:10731)
at Editor.getContent (tiny_mce_src.js:14548)
at Editor.save (tiny_mce_src.js:14449)
at Array. (tiny_mce_src.js:13372)
at each (tiny_mce_src.js:151)
at Object.triggerSave (tiny_mce_src.js:13371)
at j._saveFormState (first.js:120)
at HTMLDocument.dispatch (jquery-3.2.1.min.js:1)

We also don't experience this in Firefox. It's possible it's either how Moodle is handling the Javascript or a recent Chrome update, unless you are also seeing the error for TinyMCE because then perhaps TinyMCE is the issue. Just wanted to let you know.

I assume there's no other type of fix to this in the interim? If you are getting the TinyMCE editor issue, perhaps the short term fix is to use Atto instead, although that might not be preferable.

Dillon

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Re: Save and Show Next freezes on 2nd student

by Matt Long - Thursday, October 8, 2020, 1:12 AM

Hi Dillon,
That's really helpful! It does look like the error is specifically caused by TinyMCE. I switched my editor to Atto and that fixed the glitch. Unfortunately, most of our faculty need TinyMCE since we have a lot of linguistics courses that use specific fonts and IPA characters in their course pages. It doesn't seem like Atto has the options for that.

But narrowing down the specific cause of the problem should help the Moodle devs come up with a solution. I'm wondering if we should submit a bug report on this somewhere? I found a forum post from 2016 that mentions a similar problem with TinyMCE:
https://stackoverflow.com/questions/38613095/how-to-resolve-uncaught-typeerror-cannot-read-property-body-of-null-for-tinym

One of the comments in that forum also mentioned that the problem began after a Chrome update. I might test out the solution they mentioned and see if it works with Moodle.

Matt

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Re: Save and Show Next freezes on 2nd student

by Clóvis Amorim - Thursday, October 22, 2020, 4:54 AM

This is due to an error in old versions of TinyMCE (which comes with old versions and some recent versions of moodle).

To resolve the issue with Chrome 85, visit:

moodle / lib / editor / tinymce / tiny_mce / 3.5.11 (version)

There are two files involved:

tiny_mce_src.js (code)

tiny_mce.js (minified file)

Change the code of the tiny_mce_src.js file, in the excerpt that begins with:

impl = node.ownerDocument.implementation;

change to:

//start

if(tinymce.isOpera) {

impl = node.ownerDocument.implementation;

if (impl.createHTMLDocument) {

// Create an empty HTML document

doc = impl.createHTMLDocument("");

// Add the element or it's children if it's a body element to the new document

each(node.nodeName == 'BODY' ? node.childNodes : [node], function(node) {

doc.body.appendChild(doc.importNode(node, true));

});

// Grab first child or body element for serialization

if (node.nodeName != 'BODY')

node = doc.body.firstChild;

else

node = doc.body;

// set the new document in DOMUtils so createElement etc works

oldDoc = dom.doc;

dom.doc = doc;

}

// end

Then use some javascript minifier to create tiny_mce.js.

Purge caches for your Moodle Site

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Re: Save and Show Next freezes on 2nd student

by Matt Long - Thursday, October 22, 2020, 10:53 PM

Thank you so much! That worked perfectly.

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Re: Save and Show Next freezes on 2nd student

by Ondrej Galbavy - Monday, October 26, 2020, 3:43 AM

Thank you I did not want to migrate to Atto in the middle of school year.

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Re: Save and Show Next freezes on 2nd student

by Alex Rowe - Tuesday, October 27, 2020, 6:39 AM

Can someone attach their src and min JS files for the 3.5.11 version that they have confirmed has fixed this issue?

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Re: Save and Show Next freezes on 2nd student

by Matt Long - Tuesday, October 27, 2020, 9:11 PM

Hi,
I've attached the TinyMCE files with the changed code. We're using these on our site now.

Matt

tiny_mce_src.js

tiny_mce.js

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Re: Save and Show Next freezes on 2nd student

by Alex Rowe - Wednesday, October 28, 2020, 6:52 AM

Thanks Matt. I tested these on one of our dev instances and they work well.

Chrome on version 66 worked before the changes
Updating to Chrome 86 stopped TinyMCE from working
Applying the patch and clearing all caches has Chrome working again.

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Re: Save and Show Next freezes on 2nd student

by Raisa Retif - Saturday, October 31, 2020, 5:03 AM

Thank you so much!!!!

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Re: Save and Show Next freezes on 2nd student

by Sam Thing - Thursday, November 5, 2020, 5:31 PM

That's a bit irritating. Still returned the error after purging the caches. I had to turn Theme Designer Mode on and off before it would work :P

Working now, thanks.

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Re: Save and Show Next freezes on 2nd student

by Rodolfo Siles - Tuesday, November 24, 2020, 6:04 AM

I had the same issue with our Moodle 3.3.3 after a Chrome update back in August. Had to use Firefox to be able to move to the next student. But now, after the latest Chrome update (Version 87.0.4280.66), it is working again. Go figure!

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Assignment

Save and Show Next freezes on 2nd student