The room is 11x11x3 with no lights, and has a 3x3 hole in one corner. It is surrounded by fans to push the mobs into the pit. The light is 0, yet no mobs will spawn. I stand less than 30 blocks away at all times
I'm playing the Minecraft Crash landing mod pack, and mobs won't spawn in a dark room?
An incling inside tells me… When you are this stuck you crash out normally! When it is then it is! Like a messed up game over! But not a successful one!
I'm unfamiliar with that Modpack, but check to see if your modpack has cursed earth, I think it's from Extra Utilities but not 100% on that. If it does then you can do a ritual of sacrifice using an enchanting table and a devision sigil, which spawns cursed earth, you then need to use silk touch to pickup the cursed earth and place them in your spawn room.
If you don't have that mod then you may have JABBA installed and you can use a Diamond Dolly to pickup a spawn cage from a dungeon, or may also have the soul cage mod to create your own spawner. Most modpacks have a mod which allows you to spawn in mobs, take a look in your NEI list and see if you can find one.