Got the same issue, but it seems just to be a graphicbug. Stand under the loot and you should be able to pic it up in the "environment"-section in your inventory. Cause the loot seems to be placed on the ground, but the graphic just got up to the roof.

Was unable to pick anything up, standing over the objects which were under the ground ,the game doesn't recognize them as being in the "vicinity"..

Devil's Castle and Black Mountain also had items under the floor you can see as you ascend the stairs. Was unable to pick them up or see them in "vicinity" from the stairs or directly above them in the room they should have spawned in.

for me is in every castle. sometimes i can get it through floor..
usualy not