Mob Spawner Issues

[GumballWatterson]

So my mob spawner is a big structure, four blocks tall, not in a mooshroom island, all red, (dark), and has just randomly stopped spawning mobs. I have been at least 30-40 blocks away from it for a period of time, and nothing. The mode is on hard, I have tried switching it to peaceful and then back, and I don't know what to do. Thanks for the help.

 

[Cptqrk]

30-40 blocks away is a bit far. Consider in skyblock maps, they suggest making your beginner mob farm 20 or so blocks away.

 

[GumballWatterson]

It doesn't matter where I stand, it just doesn't work.

 

[Cptqrk]

Have you lit up all the surrounding area? Mob spawning rules will apply. Just because you gave them a nice dark area to spawn, doesn't mean they will spawn there if there are other nice dark places for them, or if the mob cap has been hit as well.

What version/mod pack are you playing? I remember there was an issue with one of the mods at one time spawning excessive amounts of a certain mob that had to be cleared out with a cofh kill command. Maybe this is happening?