I opened a mods server with my friends a while ago. I love Alex's mobs, so I tried to install it on my server. but It only spawns flies near my house, but nothing else spawns. I thought the mod just didn't work, but then my friends and I traveled about 2000 blocks from our house and found some alligators and raccoons. So I realized that mobs are actually spawning, but they just don't spawn in preloaded chunks. Is there anything that can fix this issue? Please let me know.

The mod isn't even loading up for my server.