Put the summary of the bug you're having here

What I expected to happen was...:
I would migrate my 1.21.4 server to 25w02a with little to no negative impact on gameplay

What actually happened was...:
hostile mobs no longer spawn

Steps to Reproduce:

I have tested these steps and the bug is reproduced

1. Start a server on 1.21.4
2. Migrate to 25w02a by replacing the server.jar file
3. Play on new server -> no hostile mobs will spawn