I have run into the same situation recently. Seems a problem with all backpacks. When placed in editor they fall just through until they land on ground. Also happens outside of buildings when they for example placed on a desk, they always land on the ground ingame.

Regular props like the laptop etc. cannot be put into the inventory of the player, the Chemical Detectors without functionality can. I can put them on the ground in the editor and pick them up later in the game. So it seems natural that if you can put a object into the players inventory, you can also select it from the arsenal, for example as a "misc item".

Tried out devbranch and it now shows the full pathname again.