mob spawning issue

Since the nether update i have very few mobs spawning in my farm.

All mobs?

No, i have slime, slime, slime, slime, slime, sometime skeleton, spider and creeper (2 or 3 per minute).

Before the update i had all type of mobs (spider, skeleton, zombi, creeper, witch, pillager, endermen and some slime)

 

Plz fix it.