World freezes and resets when I walk too far.

Everytime I enter my realm the game world freezes once I walk past a certain point. I can still walk around but all mobs are frozen, blocks break without any animation and nothing is saved after quitting. I tried downloading the world and playing offline, but the same thing happens.

Possible causes/additional information:

• The world has been generated about 2 years ago, but yesterday I traveled beyond the generated world and entered the new seed from the latest update. I didn't encounter any problems that entire time, the issue only popped up later that day in my home region.
• I've been messing around with the difficulty and mob griefing settings around that time.
• When traveling by minecart the freeze happens at the exact same spot every time. The minecart stops moving but I can still exit. One time chunks even kept generating when walking around, but beyond that nothing works.