Persistent sheep de-spawned

I've had this world since 1.17.0.52 Beta.  I had two fenced area, one with cows and chickens and the other with sheep (all white).  I have breed both sheep and cows at the same time, kill the adults and let the baby grow up and so on.  I stayed in the area but had my backs to the fence area to do other things like farm trees and stuff.  When I looked back after about an hour, all the sheep had de-spawned. Non of them were named tagged but I've interacted with them and should be persistent i.e. feed them or born as a result of breeding.