Re you using the latest update? (4.19.4)
The console errors may refer to an uncleared asset cache. Make sure to clear your site cache as well.
If it works sometimes, then it is very unlikely a plugin related issue unfortunately. I recall a similar issue from few months ago, then simply the PHP memory limit was set too low – as the site grew, and more plugins were installed, it simply failed at a point of execution.
Please check your PHP memory limit, and try increasing it to at least 512MB if possible.