We recently upgraded to Moodle 3.8, and we're seeing some rather major performance issues with the Atto editor when using the Safari browser, and also to a lesser extent on Chrome (MacOS). We also see this on 3.9 (using sandbox.moodledemo.net). We’re not seeing any problems on Firefox (MacOS). We don’t see this in Windows... mainly Safari and Chrome on the Mac.
What we're seeing is unresponsiveness and lock-ups in Atto when using Safari. For example, when writing on a page, selecting some text, the selecting the Heading toolbar icon, we see a stutter in how Atto reacts. Oftentimes, one has to wait a second or two for the change to take place. This sluggishness seems to be especially prevalent when using the Font Color toolbar, or any Atto toolbar plug-in with a menu. Selecting text, then selecting a color, one usually has to wait a couple seconds for the change to take place. And then, you usually can't do anything in the browser for a couple seconds or more, until it unfreezes and returns you control.
UCLA has confirmed that this issue exists on their Moodle 3.9 site.
I’m wondering if anyone else has encountered this. We created a Moodle Tracker issue for this (https://tracker.moodle.org/browse/MDL-69292). We actually determined what was causing the problem and developed a fix. We have implemented it on our site... it works fine. We’re hoping to get more up-votes on the tracker issue so this can be addressed in Moodle core.