I’ve got a problem with US weapons DLC. I played about 3 hours with N60 machine gun, then gave it to a friend to just look at it and the N60 disappeared.
I uninstalled the DLC and re-installed it to maybe solve the problem and now I lost my N9 pistol too.
If you look at the patch notes for the December '20 update, one of the known issues is this:
If another player who does not own the U.S. Weapons Pack DLC picks up one of the weapons dropped by someone who owns the DLC, the weapon will disappear for both players