Shader hangs up in Preinit/Source build

Hello!

I built successfully the 4.12 engine from source but my game doesnt start. The splash screen shows, but then it hangs up. More precisely it is in a loop in shader.cpp if I pause the debugger. It is a huge loop, and after a hour waiting, no much advance. There is advance but if you check the loop max, it will take eons to finish. I already tried to delete intermediate/rebuild, even the unreal caches in documents/appdata, but didnt help.
Any help greatly appreaciated!

thanks,
Gabor

more info: it is the debuggame configuration.
interesting that I can run the game from debug game editor config/play from editor.