The mod Witchery Resurrected for 1.12 is currently in beta. There's some weird compatibility issue I'm getting between the that and this that no one has yet reproduced where the game will load in just fine, but only mobs and menus have textures. Blocks, items, and some menu icons all have the Gmod texture missing texture.

I can provide a log on request, or contact the devs if it would help.