I just wandered over to the chest shop to check on prices and found that I had an opened epic chest waiting for me to click on "Take All and Reset". (This must have been hanging around from AotA release week.) I happened to have open a recent export (made today) of my collection, and noticed that the epic item from the chest was not listed. Heading over to the Keep, I didn't see the item either. (It does appear now that I've clicked on "Take All and Reset".) It seems that shop chest items are kept in some kind of limbo state until you click on "Take All and Reset". I suppose this could be intended behavior, but I sure am glad I figured out that my collection was one unique epic larger than I had thought. >_>
