Configuring animals (fe only parrots) for a biome works, configuring only blazes doesn't work, the default mobs spawn. Test biome config mob spawning settings for Forge and Spigot and confirm.

For virtual biomes, any mobs that are spawned by OTG at the end of population work, any mobs spawned on a timer by mc don't work. Have added a comment in the biome configs for 1.12.2 v9_r11.

*Does work for Forge, only doesn't work for Spigot.