If you're experiencing issues with skins for weapons, knives or gloves, there are a few things you can try to get them working again.

Make sure you're subscribed to the optional addons

First make sure that you've subscribed to the optional addons.

You can find the skins workshop collection here: https://steamcommunity.com/sharedfiles/filedetails/?id=2210311606

You can also access this by typing !content in chat.

If you've just subscribed while in-game, most issues can be fixed by restarting your game

Resubscribe

If you still cannot see your weapon skins, you can try uninstalling and re-installing.

1. Go through each addon, unsubscribe
2. Restart Garry's Mod and type the following in the console menu_cleanupgmas
3. Resubscribe to the addons and restart Garry's Mod

Clear stored Workshop Addons

The last, but nuclear solution is to clear the stored workshop addons and letting steam re-obtain the files.

You can do this by following the steps below:

1. Install Lambda Game Utilities
2. Close Garry's Mod if it's open
3. Open Lambda Game Utilities as administrator
4. Click on the red "Content Repair Tool" button.
5. Leave all the addons selected and then click 'Repair Content'
6. The stored addons will then be removed and Steam will then validate your Garry's Mod install.
7. Once validation is completed, Steam will then reobtain the addons that were removed by Game Utilities.
8. Restart Garry's Mod