I was on my superflat testing world and i had mobspawning on, but for some reason, slimes were very rare to come by. Same in my survival world, I spent over half an hour at a swamp biome but only got about 16 slimeballs from killing slimes. I think mobspawning is broken because usually in my superflat world with mobspawning on, I get around 10 or 15 slimes at a time. Mojang, if this is a bug, please fix it, but if not, I'm okay with it. Thank you!