While trying to get wither skulls I noticed there wasn't anything spawning (even blazes) so I checked and there were only 25 entities in total. I thought it might be something to do with the mob cap, but it was fine in the overworld (I was the only player on the server). I checked the all the config files, but couldn't find anything about nether mob cap. I tried restarting and going back and forth between overworld and nether, but then there were only 9 entities in total and it slowly climbed to 14 and after flying around a little it jumped to around 30. The server is quite old, been running since the new world height/depth and updating to the newest versions (it's on paper 1.20.1-174 now), but I don't think I changed anything in the configs/settings.