On todays 0.58 update the game randomly forces your character to put weapon away, this will force you to loose said weapon if no space or double carrying ie; weapon in bag and on back.
also I just lost a AK101 because I put weapon on back then climbed a deerstand, when I got back down from the deer stand the game dropped my ak101 and put my UMP45 on my back when it was originally in my bag. IMO this is a game breaking bug.