Since the latest patch 1.3 my guns are partly invisible for example I only see the magazin, scope and silencer but the main body is missing.
That's actually quite annoying, please fix ASAP

Apparently 1.3 changes some paths to configuration files, and mods that made changes using the older paths are no longer able to supply textures and other resources.

Got any gun mods? Try removing them and see if that fixes the problem. Mod developers are making changes to address this conflict; check your mod sources.

Update all mods. Update the Customizable Unique Weapons mod. In my case, the conflict was caused by Unique Weapon Customization. If that doesn't help, remove all mods that interfere with the weapon and check if it helped. If so, install them one by one. After each mod installation, check if the problem has gone away. If not, remove all mods and install them using Vortex. If you try the last option and you had a lot of mods, install Vortex, find the game in it and install Simple Mod Mergen for Vortex first, then the mods that interfere with the weapon one by one. :)
:)