Advanced Layout Builder not working after update

Hello,
I posted this in someone else’s thread last night but it seems to have gone quiet, so here I am:

Randomly yesterday I lost all RevSlider functionality in the middle of working on a slider. I went to save my changes and received an Ajax Error 500 (even though I had just successfully saved it 70 seconds before). No other functions would work either, like duplicating or exporting slides. A similar issue I had in the past was resolved by updating the theme, so I checked for updates and installed 4.0.1 (upgraded from 3.8.6). Even after update, Revolution Slider wouldn’t work (not sure if related to the theme but nothing else had changed internally to cause the error).

Perhaps the bigger issue now is ALB won’t load; the loading icon just keeps spinning. I cleared my cache and managed to get it to load once but it wouldn’t let me edit any elements (the normal editing dialogue boxes show up blank). Checked and updated to 4.0.2 and no change.

The site was supposed to be launched last night but I can’t do so until final edits are made. Any advice?

Thanks!