Named tagged animals disappear

 I have been playing this world (seed-1504192002) a long time, but now whenever I enter it all my tamed pets and mosts of the mobs are gone. The leashed pets just disappear.... The iron Golems that I created gone.  Cow, villagers, horses gone....This hasn't ever happed in any of my other worlds, but it's constant here.  There doesn't appear to be any evidence of an attack..no chat messages, no xp on the ground....no mob drops