My pandas have been despawning over time when they get unrendered because I travel away from them. The pandas were bred by me several versions back and already had name tags applied to them. Very recently, I had a villager disappear from my village that is completely contained and has no way for anything to kill him. He also had a name tag applied and was leveled to max level trades. This disappearance occurred at the same time as another panda disappeared. I think they are in the same chunk but they are not connected rooms so they weren't killed. I also had a bunch of sheep despawn a few weeks ago that I had bred (but did not have name tags).