so any time you "engage" of coming out of combat and continuing to move, this is what tells the game you've finished looking at drops.
same with chests, if you find a check you need to engage to start moving again, if you don't engage the drops should stay there.
the exception is maps, where if you complete a catacomb by exploring all the spaces, you get rewarded with a map, or multiple maps if in a group. these have a habit of disappearing especially if the last tile also contains enemies