Follow-up. Downgraded to 7.31 and problem resolved. Video had periodical mild brightness variations. We use a Aver cam-520 and have had no technical problems with recording in the past.
I just upgraded to latest version (7.39) and now the black side bars on both sides of the preview screen periodically flicker (off grey about 1-2 times per second). Extremely distracting! Since this was the first time I have run it (and it is actively live, I do not know if it is affecting the final video.