Well, that's interesting, something with cubemaps or more precisely only one cubemap (purple texture like this suggest that this cubemap is missing). I don't really have a solution for this besides restarting gmod and praying it will fix it. Or disabling addons? redownloading the map? no idea, you probably already tried this.

Thanks for the info, at least they are very minor issues so I think they are quite easy to ignore.
The map was quite interesting to explore and I think that you did a great job with it. You should definitely keep it up!

Thank you