That's a bug with a older version of Adventuron. It was fixed over two weeks ago. It doesn't affect the gameplay, it just affects when loading from a savestate (doesn't render treasure objects in a list). If you type LOOK, the object will reappear. The object was never missing, just the print doesn't work properly on a rollback (fixed long ago).
Other than the rollback treasure printing bug, it should still be working. The rollback bug is down to the "point of no return" lasting for several moves. That's a game design choice.
I did reach out to the delver devs a while back for them to update, but they haven't updated in quite a while. Hopefully a fix will arrive soon.