I have 2 mob spawners and I very rarely get a single mob spawning in either of them. Others have claimed not to have an issue. I have checked the obvious things, biome, darkness, distance from island center, but nothing seems to work. Any help would be appreciated.
Don't really have a tips for you besides the obvious, make sure you don't stand too close to the farm but also not too far. Otherwise it just comes down to how many mobs are there currently alive in the world and how many players are online.