If anyone is having issues with missing textures in reflections and they use AMD graphics, I finally found why it happens and a workaround to fix it: Here's the bug report explaining why it happens: Facepunch/garrysmod-issues#5755
- Download dxvk-x.x.x.tar.gz from here: https://github.com/doitsujin/dxvk/releases/latest
- Extract it somewhere. You will need something like 7zip to open it.
- Copy
/x32/d3d9.dlltoGarrysMod/bin. You can access yourGarrysModfolder by right clicking the game in Steam > Installed Files > Browse - Launch the game.