Tamed Animals Despawning

Me and my partner have a realm and have been playing on a new world for a couple of weeks. I tamed a fox, then one day it dissapeared. I didn't think much of it as maybe it got out, then I tame another fox and name tagged it, kept it in a secure room. I notice one day that its gone. Then i come on 2 days later and my horse and my donkey (also with a name tag) have both just dissapeared. Please fix this, it is really ruining the game for us.