On a number of occasions, I've had an item disappear seemingly into another universe, and then at some point in the distant future, return.
Example, I've got a remote for a receiver. I was taking the batteries out to place them in the recharger when I dropped the battery cover. I thoroughly searched the floor; and the computer desk, removed all items, looked behind, pulled the computer out thinking maybe it hit hit the top of the computer and fell behind, nothing.
For years I just put up with no battery cover; a bit of scotch tape to hold the batteries in. Then recently, I was vacuuming the floor, in the same area where I originally dropped it, and searched, and there it was.
I've had this happen more than once, but this instance is the most impressive to me because of the thoroughness of the search I performed looking for it.