When creating a new world, or just trying to play an old one, the world generates successfully, but then I get stuck on the "Joining World..." screen, at which point my Javaw.exe runtime process stops responding. I checked the game output in the launcher as well as the launcher log – no crash, and the game seems to think it has already loaded in the world successfully, and then immediately saves all chunks and waypoints as if it were pausing, at which point my Java runtime process would freeze.

BTW, although it does not let me choose this in Affected Versions, lately I've been getting this issue all the way down to MC version 1.13.