Thanks Troy and everyone for your encouragement and suggestions. Ultimately, I did find a solution that worked, though it really shouldn’t be necessary to do it this way.
I deleted ALL of my renders and opened the final edit, which somehow corrected the black frames issue. Whenever I tried to rerender a section, however, the black frames would reappear in various parts of the film. So I deleted all renders once again, held my breath, and exported a full AVI without rendering.
Somehow, this worked. I then placed the AVI in another Premiere Pro timeline, added my letterbox, and rendered again. I hate to render twice, but the compression wasn’t really noticeable and it allowed me to escape with my film intact.
Phew.
It’s good to hear Premiere is aware of this issue as it greatly persuaded me to look at other editing software if these bugs persist. I love Adobe’s entire suite of software, which is why I use it. But editing is difficult enough without the software constantly working against you in unpredictable ways. I’d prefer they work out these bugs before adding any new bells and whistles to the next version.
Thank you again, and hope to see some of you at the festivals.
Best,
Nathan