My internet went out so I decided to launch my game (which I did in offline mode.) I was goofing off with spawn eggs and tamed a cat; however when I looked at it my game froze with "Waiting..." over the cat's head; I had to kill the java process.

I suspect this has to do with not being connected to the internet and whatever does fetching of names blocking the game thread.

My version might be slightly older than the latest (I have PetOwner-1.8.1-1.17-rc1+.jar), but I don't see any significant changes to that logic since the time when I downloaded it.