Custom mob spawing issues (Not spawing in mushroom fields)

Hey! I've been implementing a custom mob into java minecraft, and my issue is that where I want it to spawn naturally (mushroom fields) it just doesn't. 

I've tested it by just changing to location to a plains biome and it spawns there naturally just fine. My only guess is that it's classifiying it as a hostile mob somwhere, but I didn't find anything in my procedures or classifications to make it as such. Any ideas would help me out, thank you!