The doors appear to be invisible. Not sure if it's another addon causing it, but it's not happening on any other maps I have installed from what I can tell.

I don't know what could be the problem, I don't have any problems with it and others with whom I played on this map.
Maybe you have a file conflict in the root folder of the game: Garrysmod/garrysmod/materials

I believe it was a conflict with my addons. Same thing happened yesterday, and restarting the game fixed it. Could be the number of addons I have installed. I should probably go through and get rid of some stuff to lessen the load the game has to undertake to prevent this from happening again.