Popular Member. The spawner mechanics require the presence of a player, chunk loaders will not activate mob spawners.

Do mobs spawn in loaded chunks without players?

As long as the world is open (i.e. running on a server), the spawn chunks will remain loaded, whether or not anybody is actually in them.

Why are no mobs spawning in my grinder?

The game difficulty does affect the spawn rates of monsters.

If you’re in Peaceful, no mobs will spawn EVER. Change your game mode to a higher difficulty. Stay at least in Normal or Hard mode for effective grinding.

Mobs can’t spawn in water, even from Monster Spawners! The special rule of spawners is that they can spawn mobs in midair; their spawns still require appropriate (lack of) lighting and an empty space, but they do not require an opaque block underneath like normal monster spawns do.