When I was in a lake/pound (whatever you want to call it) I began to swim, guess I went in to far. When I started to swim I saw a floating pistol, then a floating M4. I asked my buddy if he saw it and he did not. I then checked my inventory and saw my pistol and M4 where gone. To my buddy my character looked to still have a pistol and M4, but in reality I did not. Also I was unable to loot my m4 and pistol back. My buddy could not even see them in the pound. So I just lost the loot.
Also not sure if it is only happening with weapons.