Our island is pretty new; we placed down grass for passive mobs and created a traditional grinder for hostile mobs, but neither passive nor hostile mobs ever spawn. We checked everything we could think of in the grinder-- it is very dark and not too close to our base. Please help us figure out what's wrong. Thanks!
Spawn rate is already set rather low for the passive mobs, so you would be lucky to see them (Unless AG+ is different than AG standard), but as for the mob grinder, there were probably too many hostile mobs already spawned on the server. The reset cleared them, giving the server space for hostile mobs, which you managed to spawn.