Even after feeding ,name tagging, or riding a mob the mob would eventually despawn. So far many cows, horses(including skeleton horses) and foxes have despawned for some reason.
MCPE-120469
Passive mob that shouldn't despawn despawning.
Resolved
Duplicate
0
This issue has already been reported. Duplicate MCPE-21416.
You can add additional information or just vote for the solution to this problem in the specified report.