Hate to say it, but some bugs involve mission critical items and the game gets sour real fast. If you see any of these issues revert to an earlier save, most are not recoverable and accumulated open ended quests go bad in a hurry.
I've explained it like this to people that find these "misplaced" bugs and ask for help. Look at boundaries stacked like absolute boundaries and some softer boundaries like fences that make up most surfaces. If an object lands above the fence -no problem. However, if it lands between an absolute boundary and a fence you see it, but can not pick it up - this happens when the "floor" has special effects and the game engine "misplaces" the object, some boundaries are quite dynamic. And it can happen to anything, even demons and once a player! If you don't see the item/demon at all it may be outside the absolute boundary, which should not be possible, so consider another opaque fence because it still shows up on tactics and you know it is there, not in limbo.
The other issue with demons and loot is "stuck on a fence": if the demon wiggles right or left targeting detects it, but on the boundary the game engine is "confused". When loot happens to land on a vertical object, it does not matter how close you get even if you see the loot -can't pick it up, wrong side of fence, so to speak.
Seeing this behavior I was thinking of proposing a right circular cylinder that covers anything w/in 1 meter or so and extending to the character's height + 1 meter and activates a buoyancy effect to float the object to the player if it is stuck/out of reach. This might also help when loot falls behind or inside rocks. The key is to override the boundary for a moment and recover the loot. I've seen a lot of these as you can imagine.