My antlion guard and the human grunt (from half life source) spawn invisible. They still attack me, make sounds, die, and other NPCs see them. How can I fix this. I think they may be invisible because of something from gmod.org
Wipe your garrysmod folder and do a clean install?
Or go to any addons that have models or your main garrysmod folder and search for those models. Then when you find them, delete them.