This issue happens on the current development branch of Garry's Mod - usually it is only fixed by restarting the game.
It will probably be fixed if you change from the dev/64-bit branch back to the stable version of the game.

github.com/Facepunch/garrysmod-issues/

This issue happens on the current development branch of Garry's Mod - usually it is only fixed by restarting the game. It will probably be fixed if you change from the dev/64-bit branch back to the stable version of the game. https://github.com/Facepunch/garrysmod-issues/