SFM (Hammer) - Missing HDR lightmaps

[Vinnco]

Hey guys, I'm currently having some issues with a custom map I am working on for an SFM animation. It's quite simple - I compile the map and when I open it in SFM, I get the "This map is missing high dynamic range (HDR) lightmaps..." error. I am not new to mapping, have made maps before that works perfectly with HDR, but I really can't get this one to work...

Some info about the map and what I have tried so far:
1. The map is made in the Hammer that comes with SFM
2. I have "light_environment", "light", "logic_auto" and "env_tonemap_controller" entities added in the map
3. The whole map is one big empty box (9960 x 9936 units width and height) supposed to be for a scene in space. It's a hollowed box with "tools/toolsskybox" texture everywhere. There is also a 3d skybox added with a sky_camera and lights added inside it as well.
4. Compiled with the simple compiler with all set to "Normal" and the "HDR" box ticked - same issue
5. Compiled with "Final" under the expert compiler - same issue

Any tips found by searching have not helped me, so I hope someone here might have an idea. If you need more info, just ask. :)