Gmod is screwed so here we go. i figured out a fix (Updated description) So. figured out something adding new addons to your pack via the sub to all button Will break your currently installed addons less than if you just got them but it's still pretty bad. if your addons break use something to screenshot console to check the duped ones and resub to them manually One by One. that's the only way it has worked for me Text tutorial here. Uninstall all addons (make a collection if you want to keep some) , change steam to steam beta, restart steam, find collections (unless you already made one) and sub to each addon and it's dependencies individually. once done it may be worth closing steam entirely and restarting to speed up the download of addons though idk if this works Please do leave comments if it Did or Didn't work and run me through what you did i'll try to help.