Same here, only after a patch. I think it has to rebuild the ShaderCache.cooked file, but I'm not positive on that. Usually takes me around 6 or 7 minutes after a patch.
Lag is ruinin' my 'mershun! A society grows great when old men plant trees whose shade they know they shall never sit in. There is only one good, knowledge, and one evil, ignorance - Socrates Member of the Old Guard, keepers of the game's history