Hi Hades
You mention a consistent crash when entering Pet Battle. Seems that is something Blizzard is looking into. Hard to say if that would be related to your other disconnect issues. Check this thread:
https://us.forums.blizzard.com/en/wow/t/getting-dc-at-the-start-of-wild-pet-battles/684563/9
Now you said you disabled addons - they don’t disable well and can cause issues even when disabled. As a test you might try a full UI reset:
As I mentioned this is a test. If it doesn’t help simply remove the OLD from your original folders then delete the new folders the game installed. This will return your original settings