I could not find another example of this happening. Side note: I've watched all of your gmod videos. I haven't even seen someone get a single kill with the P90 in days, despite all of our officers having them. The only way I could get around fixing this was asking to someone with a mod menu that has the option to remove all weapons of a player to remove my guns so I could go to the nearest Ammu-Nation and properly unlock them by buying said weapons, thus being able to see and hide them on my gun locker. Back then, the P90 was actually part of the meta, which is hilarious.
Although most of them go away (Railgun, fire extinguisher etc) some of them do stick on your character, such as the Widowmaker, Navy Revolver and others, but they don't show on your gun locker because you technically don't own them. There's this issue with weapons that are given by modders, though. They should've just added it as an option to the Context menu you open to assign yourself CEO. On the opposite wall, there's another gun rack, that will let you hide weapons you don't want. IDK where it is normally, but for me, it's in the truck you go to in your underground bunker to make MK2 weapons.
You can just hide the weapon in your weapons locker.
