Are you still having problems? If you are in the location where you first spawned in, try going 130 or so blocks from your spawnpoint and try again. Since it is classified as an entity, it may be victim to that bug where some entities will disappear after a while for no reason. In my worlds, this only happens in the spawn chunks. This includes itemframes. They ALL are still there, they just aren't visible and cannot interact with them. They will appear again at seemingly random times, so I build outside the spawn chunks. I think the /setworldspawn command can trigger this bug as well.