When I have optical camo backpack equipped, I get a weapon bug. Aiming down sights is wonkers.
In 3rd person, all I see of my weapon(s) is the supressor and the butt of the gun.
The work-around for this bug is to stand up so my character no longer is in camo-mode and if required, switch weapons around, by pressing 1,2 or 3.
Until the whole weapon is rendered as it should be.
Needless to say, I stopped using optical camo.
Heres the link to pics
https://imgur.com/a/ro54UIT
First one is an assault rifle, the second picture with nightvision is a sniper rifle.
Just to confirm that you aren't alone with that problem. I get that too and do the same things to resolve it, although it's frustrating to have to do it when you're close to the enemy trying to stay stealthy.