I tried to isolate the biome by making a superflat, but i got spawns from that. Here's my code if you were curious
2;1x7,50x1,1x80,1x78;140;mineshaft(chance=0.01),decoration
It's most likely not the biome tags cause i saw normal ice plain spawns in the superflat. My top two layers were snow blocks and snow layers, so that's not the problem. My guess is that all the spikes were not providing enough open space to spawn a group of pokemon.
Mods used:
Forge 10.12.2.1121
Pixelmon 3.1.4
VoxelMap 1.7.2-1.0
(and about a dozen others)
Seed: -7713472810437777034 default world type
location (-291 71 520)
Anybody else notice something like this? Should I forward this to the bug reports or is it already known?