Vanilla Aquatic Mobs Not Spawning

Hi, I'm running a Forge server with a handful of mods. Initially there were no issues with aquatic mobs, but at some point they just stopped spawning, besides modded ones. I copied the world and configs into singleplayer, and they do spawn there, but not on the server. I can't fathom why. I don't want to try binary mod removal on the server itself since a lot of blocks and items will be deleted, but the inconsistent behavior between server and singleplayer is very odd and makes it difficult to test. Not really sure what to do, any suggestions?

My initial suspicions were that it could be from Cold Sweat, Cataclysm (possibly killing the abyssal boss broke something since it said it enabled golems to spawn in the ocean), or Serene Seasons, but I didn't need to remove any of those in single player to get them to start spawning again despite copying all the world files and configs directly from the server.