Final update: When to Delta.com and selected the seats, paying for the one that was for the pax with no status. Showed up fine on the reservation page after purchase. When I received an updated receipt from Delta, it showed my companion in their seat, but my seat was now unassigned!!! When I went back to the seat selection page, I couldn't select ANY seats now for myself, as they were all X'ed out, meanwhile my companion is showing in his seat.

I called the Delta Plat desk and, after the agent being on hold with AF for around an hour, she managed to get me my seat for no charge. I'm not sure how the systems talk to each other, but there was definitely something wrong here. FWIW, before I called Delta, I could go to the AF web site and select the seat, though it was still making me pay for it.