All sorts of mobs keep despawning when they shouldn't be

So I play on Minecraft pocket edition and my mobs keep despawning. Mobs I have tamed, mobs I have bred, mobs I have dyed, mobs I have put things on, and mobs I have named. No matter what I do I can't keep them from despawning. Know I'm pretty sure this isn't how mob despawning works and I'm fairly certain something is wrong. I'm hoping someone sees this and can fix this please, I have already lost 2 saddles and 3 name tags I don't want to lose more.