Summary
My console is being flooded with "Mob type ZOMBIFIED_PIGLIN not found - removing mob [UUID]"
Steps to reproduce
Going to the nether. That's all that causes this to happen. Note, this seems to only happen with naturally spawning pigmen, though. When I spawn them in with eggs it works fine but then I move over a few chunks and suddenly the server is frozen.
Current behavior
When I have ZOMBIFIED_PIGLIN under VanillaMobs my console is flooded with this https://pastebin.com/w2JweU6Q and my server crashes. Even sometimes without ZOMBIFIED_PIGLIN under VanillaMobs, this still happens. I have tried deleting saved data and restarting and it only solves it temporarily, once a player returns to the nether the exact same issue happens again and the server crashes. The only solution I've found to this is to delete the nether world file and disable portal creation through CMI.
Server log file
Debug log snippet