Hello, today after a 24 hrs the server running I noticed that mobs stopped spawning even at night! I tried restarting the server and changing the difficulty to hard non of those fixed the issue. I think mobs are spawning in new chunks but not in ones that already exist sadly. I'll be happy to provide any information if I can.

Update:

I think mobs are not spawned in chunks that are loaded for long period of times. When a given chunk is unloaded and then loaded there are mobs spawning for the time being then they stop again