Ever since the update yesterday, my realm has been reverting back to previous states. Anything done in the realm will not save. You can connect to the realm for 5-15 minutes before it disconnects you. Once you log back in, you are taken back to where you were when you logged in the first time. (Let's say you log in and you are at home, you then decide to explore a cave or something. Once you get kicked and rejoin, you are back at your house and anything you modify is reversed.)

I wasn't having this issue with 1.17.11.

If you need a visual, I will gladly turn on my OBS and try to capture it happening.