End whale, yeti and cindershell are not spawning, but the rest of the mobs do. I use the mod on aternos and i dont know how to solve the problem.
I tried in vannila too and they dont spawn either.

End whale seems to be from a broken tag (#forge:is_end has been replaced with #forge:is_outer_end), making a datapack to replace the tag has made them spawn naturally for me. Yetis seem to spawn rarely but despawn very quickly, and Cindershells i haven't been able to find a fix for.

i have discovered that the tag might be broken because of another mod (biomesoplenty in my case), try to check your datapacks and make sure everything is formatted correctly

Fixed in 6be8496