Some animals not spawning, horses disappearing

Hey guys. Whenever I try to spawn spiders, zombies, pigs, sheep, and cows, the animals don't spawn but it sounds like they are. When I use the /spawnmob command, the same thing happens with the same mobs. The rest are fine. I can't get these mobs to spawn with monster spawners either. Horses will spawn, but whenever the chunk unloads, they disappear. I've turned on mob spawning in the server.properties file, but what confuses me is that the animals which aren't spawning are random ones; some are passive and some are not. I've been trying to fix this for a while but I honestly have no clue what I should be doing anymore. Thanks for any help in advance!

 

I think there is a thing in essentials that block certain mobs send your config

 

These would be the lines you're talking about, but unfortunately I don't think that's the solution:
# General physics/behavior modifications
prevent:
lava-flow: false
water-flow: false
water-bucket-flow: false
fire-spread: false
lava-fire-spread: false
flint-fire: false
lightning-fire-spread: false
portal-creation: false
tnt-explosion: true
tnt-playerdamage: false
fireball-explosion: false
fireball-fire: false
fireball-playerdamage: false
witherskull-explosion: true
witherskull-playerdamage: true
wither-spawnexplosion: true
wither-blockreplace: false
creeper-explosion: false
creeper-playerdamage: false
creeper-blockdamage: false
enderdragon-blockdamage: true
enderman-pickup: false
villager-death: false
# Monsters won't follow players
# permission essentials.protect.entitytarget.bypass disables this
entitytarget: false
# Prevent the spawning of creatures
spawn:
creeper: false
skeleton: false
spider: false
giant: false
zombie: false
slime: false
ghast: false
pig_zombie: false
enderman: false
cave_spider: false
silverfish: false
blaze: false
magma_cube: false
ender_dragon: false
pig: false
sheep: false
cow: false
chicken: false
squid: false
wolf: false
mushroom_cow: false
snowman: false
ocelot: false
iron_golem: false
villager: false
wither: true
bat: false
witch: false

 

TheGoldenGoal List of plugins?

 

Plugins:
Citizens with Sentry and Builder, WorldEdit, iConomy, ChestShop, CraftArrows, CoreProtect, MassiveBooks, Lockette, Modifyworld (with no restrictions on spawning items), Essentials with Protect (not on), Chat, and Spawn, Multiworld, PermissionsEx, SurpriseBags, WorldGuard, PwnFilter, MonsterBox, Factions, ColourMotd, BukkitCompat, StickyNotes, Minecart_speedplus, Playerheads, and mcore.

 

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