This is a followup to a comment on the main page:

Okay, so I've gone through the process of decompiling the .gma, unsubscribing on my client, loading the entire map and its contents into a folder named "gm_cyan_dreampools" and cut that into my clients addons folder. I Opened the map with mat_specular 1 on, at this point there appear to be no cubemaps effects. I run buildcubemaps, it completes successfully, map reloads, i can see cubemap effects properly. I compress the gm_cyan_dreampools folder into a .zip with windows and upload it to my server. I delete the uncompressed map folder from my addons folder. Unpack it inside the server while the server is stopped, removed all related workshop collection information as well as removed the map from the servers collection workshop page. Started the server, server appears to load map successfully. I join server and get the "Map missing" error. I have FastDL syncing enabled on the server with a (net_maxfilesize) 500mb max file download limit. (I'm unsure if source engine/gmod even allows us to change this value above 30.) I resubscribed to the map on my client and rejoined the server and was given "map differs from server".

After trying the above, i reloaded the map in single-player just as the subscribed workshop map and not decompiled, I ran buildcubemaps and was given "maps/gm_cyan_dreampools.bsp is not writable!!! Check it out before running buildcubemaps."

So if i had to take a wild guess without any real knowledge about how the workshop handles maps with cubemap files or .bsps containing cubemap information. Id have to say for some reason the cubemap is being blocked or broken before and or after uploading the map to the workshop. Or perhaps the information is not being placed into the .bsp correctly before the upload process. (Not a insult<3)