I am also seeing the of huge changes in sun brightness - I noticed it mostly when scrubbing the time of day in the sky sequencer. Also in VR, I can only see the sky in the left eye on the Vive, regardless of whether “share buffers for VR” is on or off.
When something goes wrong with it also seems to be doing a hard crash, there isn’t the usual crash log window pop up that you typically get when UE4 crashes.