Hi Craig - thanks for the response. Yes, I have the very latest SBIG drivers and SGPro version installed. I did a clean install on a brand new Windows 10 machine just yesterday. You are right this seems to happen mainly on short exposure bias frames, but I have seen it on longer duration flats, darks, and lights also, though not to the same degree.
I also put 2 second delays between each frame but still see the same behavior. I also changed cameras from an STX to an older STL and the behavior repeated itself last night also.
Chris