Yup...

welp. that's gmod for ya

Shit, i dunno what to tell ya, man.

its not installed

Do you also have L4D1 mounted?

i did, didn't work

Restart the game then?

i unmounted l4d2 and nothing changed, the purple appears underwater and console is still spammed

As it turns out, having L4D mounted causes this because since this map has all the textures and models needed are packed into it conflicts with the mounted ones which cause THIS to happen.

Unmouting L4D fixes everything from this, to invisible models errors being spammed in the console.

I'm trippin. I swear the picture is moving super duper slowly.