Large Chest Break into Small Chest at random intervals when left alone

When I place two chests together, they snap into large chests. If I leave them alone, eventually they will snap back apart into small chest and stay that way (until broken and replaced). No materials inside the chests are affected: they just stay in the chests.

Oddly, it only happens on the east-west axis, not the north-south. It happens in various areas around the map.