While checking out the newest Snapshot, I found that (at least) the following entities temporarily seemed to visually disappear (but randomly reappeared later):
Item frames
Armor Stands
Various animals, tamed and untamed
Related issues
Comments
[Mod] Neko
LuxiKeks
They reappeared after returning, but were initially invisible when logging in.
Did the entities disappear after dying or after leaving the area and returning?