Hi Hannur, after a careful look at the code, we can’t seem to find the exact cause (specially as we can’t repro in-house); however I do a workaround for you:
Try changing in the file Engine/Shaders/ShaderVersion.usf, the guid that’s there (just change any number or add more characters). This will force recompiling all shaders.
We’ll be adding more error checking so this doesn’t become a blocker for 4.8.