When they show up like that in Atlas it means the node/object that they used to be got deleted from the database. Deleted objects are purged every night when the maintenance runs at 2:15 am so unless the change just happened you are pretty unlikely to be able to find out what it used to be. If you hover over the object it would tell you the NodeID that it had, and maybe if you look at the other nodes that were added around that time it could give you a clue?
