I'm playing an existing world, but while mapping out new areas I've noticed that the areas are completely devoid of wild life. If you camp in the area for a day or two, maybe a single sheep or chicken will spawn so it's possible that spawn rates are just extremely slow.
A slow repopulation rate of an existing area makes sense once all animals in the area have been harvested, but for new unexplored areas to be completely barren of wild life doesn't make sense at all - you would expect the wild life to already occupy the area.
Attached are screen shots of a grassland field in a new area I travelled to 32 chunks or more away from an area I previously occupied. I sat in the area for 5 minutes and no animals appeared anywhere.
Note: This only started happening as of the 18.104.22.168 update, because previously when you went to new areas wildlife would spawn immediately.
Possibly related to my other ticket,
MCPE-29526, since spawn rates in generally seem to have been overly adjusted downward in the last patch.