Mounted: CS:S, Custom files, more; no issues other than the cubemap issue and a shader issue involving the map's water (which I ignore since I never use it in the scenes anyway)
Its no mystery I have arbitrary edits to my Source Filmmaker over the many years I've worked with it; considerably more than too many to keep up with.
Somewhere along the lines something must have overwritten a core engine element or something because things with env_cubemaps seem to be reflecting something that doesn't exist
Is there any possible way to replace GLOBAL env_cubemaps, and if so whats the file path so I can find it and remove it; I've already spent an entire day browsing folders and testing via trial and error to no avail.
Regarding SFM, I have many games mounted and have modified each as I've seen fit, sometimes however blindly overwriting things over the many years.
Envmaps built during compilation are saved inside the .bsp, hence why you weren't able to find them in your file browser. Does it look normal in the game you took it from? Honestly the best advice I can give is to just recompile the map yourself.