I have experienced the same issue on 1.12.1 I built 3 mob grinders in survival none of which work I know the designs work because they worked in previous versions. I have tried lighting all caves below surface and killing all mobs but nothing spawns in them or in the rest of my world I am playing in hardcore mode and haven't slept in game 20+ days been both underground and above ground and have only seen drowned mobs no creepers, skeletons, spiders, or zombies.
Joshua Dylan Lane
I have experienced the same issue on 1.12.1 I built 3 mob grinders in survival none of which work I know the designs work because they worked in previous versions. I have tried lighting all caves below surface and killing all mobs but nothing spawns in them or in the rest of my world I am playing in hardcore mode and haven't slept in game 20+ days been both underground and above ground and have only seen drowned mobs no creepers, skeletons, spiders, or zombies.