yes, it will freeze your water or get rid of your ice and snow, but no biome mobs will spawn. I know you're going to say that it takes time for passive mobs to spawn, but it shouldn't take very long to get slimes in swamp biome's. and after waiting for 30 minutes, I haven' gotten a single one. and yes, it is a swamp biome, and it is the right light level, elevation and, distance. I don't know what isn't working, but it isn't.
Hm, that will be looked at. If you're just looking to get slimes, mine works great in the plaines biome, just use that for now until the problem is fixed.
I was hoping to avoid making a massive platform to find spawn chunks. well time to grind a few K cobble