I’ve come across those threads as well. The tighten/collect seems to be causing issues for multiple people, so maybe it needs to be looked into?
I had already tried deleting the cache. For some reason on plesk, I always have to go to the CLI and change the ownership of the cache files for things to work normally again. This started happening after having to revert to a backup in the past.
As this is a live version of mautic that I actually need running, I’ve reverted back to 2.16.3. Would there be a way to create a fresh install of V3 and link it to the existing database? When I create fresh installs things seem to work so much better.