There's a difference to MC-92958 though. He had new chunks appearing and i had ones that were already loaded
You used the @e with no limit, meaning ALL of the entities displayed hearts so that's 900000*n, with n being the number of mobs, even in unloaded chunks
Also, when changing after re-opening it, it reverts to default
There's a difference to MC-92958 though. He had new chunks appearing and i had ones that were already loaded