no the map doesn't require HL2 or CSS

This is probably one of your active addons conflicting with how the map is built.
"r_3dsky 0" shouldn't fix anything because there is no 3D Sky in the map, yet, it does.

Can you try typing in the console "ent_remove_all sky_camera" while on the map, and tell me what does the console say in return?

Look this is a simple fix, I'm not going through 100+ addons to figure out which one breaks it, this fix is good on this map because there is no 3d sky so nothing sexy to look at, however it fixes it as you can tell in the images. What this does is remove the skybox completely from what I can tell and instead just gives it a plain look

Indeed, it's a simple fix. To be honest, if you want to look through your addons or not is your own problem, I didn't even suggest doing it in the first place.

I'd be very happy if you could type the command listed in my previous post into your console and tell me what it says back. To put it simply, I think your game is creating a sky_camera entity in the void because I haven't placed one in the map, so it creates this wacky effect. If your console says it has removed 1 sky_camera after typing the command, it would confirm my theory and I'd be able to fix it easily.

Why do I ask you to do this? Well, I've thought about overhauling the map, and if I know EXACTLY what to fix and how, it would greatly increase the chances of it happening.