Generators Not Releasing Slots Without Kill Self
If a generator spawns an item and that item uses "delete self" or is expired via lifespan, then the generator will never respawn the item naturally or on use even if the delay is up on that slot. It only frees up if the item "dies".
Summoning Stone (38025) + Jester (37289) You'll need to change the jester to delete himself to see it in action.