Short version: Unless players aim somewhere (VERY) close to themselves on sky, they cannot see it. They see messed up blackness instead.
Long version: In one of older -unanswered- posts:
Sun is correct, surfacelight thing is correct. But rest of skyshader has gone mad.
Tried increasing distancecull, blocksize. Didn't work I guess that it's something closely related with struct-detail brushes, but don't know exactly.
Help is appreciated.:beer:
An actual mapper could give you a much reliable feedback, but here are my 2 cents... Skyboxes can conflict very easily with certain shaders, fog would be one notable, in certain tests I've run into, a map where both the skybox and fog were visible caused the furthest corner of my skybox to clip through the void... in another occasion a playermodel with a shader to invert the normals or certain polygons caused half the skyboxes of a number of my maps to become void (it sounds ridiculous, but did happen)...
a suggestion?... selectively remove your shaders one at a time to find out wich is conflicting with your skybox. This may be caused by other things too, like weather, effects... since these trigger shaders...