Apple's moderators need to stop deleting messages from this thread. Their actions are making it nearly impossible to follow the reports and information that are coming in from users.
For instance, anyone reading this thread today would have no idea what caused my issues (and that of other posters) to recur, after appearing to have been resolved by 10.15.3. So in the interests of actually trying to help other users (and Apple, if they actually care), here's what happened:
About a week after updating to 10.15.3, my issues had largely disappeared, so I posted, letting the board know that. Another user, whose post has since been deleted, replied that I should wait and see, as he had also thought 10.15.3 resolved the issues, but they later recurred when he restarted his NAS and his Mac. I told him I'd try it, and unfortunately, upon restarting my NAS and Mac, the issues started recurring.
So, for those folks who believe 10.15.3 fixes their issues, have you tried restarting your NAS and Mac yet? For me, at least, the problems started up again immediately, and I now have to do a hard reboot (holding down the power button) of my Mac at least every day to get my computer functioning again. When the NAS issue occurs, it causes apps (including Finder and Chrome) to freeze and be unquittable. Folder on my NAS appear offline in Finder, even though TimeMachine backups are still happening.