Hi Geoff, I don’t have a solution for you yet, but I can commiserate.
I had a shoot in a small room in front of a BIG window on a partly cloudy day and things got real ugly real quick. Only a single camera shoot, but my white balance was all over the place as the sun would peek out from, then go back into clouds. I’m trying to match this interview with another one I did in the same spot on a completely cloudy day in front of the same window. I’m following this post to see if others have a similar experience and what advice is offered.
Thanks for posting!