PlatinumGoon

So i recently started a minecraft server with my friend, but for some strange reason no undead mob will spawn in the nether including zombies, skeletons, blazes, withers, zombie pigmen, etc. i have no plugins installed and domobspawning is true, the weird things is other mobs that aren't undead spawn perfectly fine, the difficulty is hard and undead mobs spawn everywhere else, if you try spawning a zombie pigmen in the overworld it works but in the nether it doesn't, you can't even push a zombie though a nether portal.