Flight is operated by Envoy as American Eagle. Booked it using BA avios, in coach at the 7500 avios level. Obtained AA PNR, added my AA FFN to obtain my AA CC holder benefits. Itinerary shows in "my flights" on AA.com and in AA app, and is "ticketed". However, when I go to select seats at AA.com (regardless whether through full desktop site, mobile, etc.), I get the following message:

"We’re unable to assign seats for everyone. Please check back or we’ll assign seats at the airport."

This is interesting because when I go on AA.com and search the same flight as if to buy a paid ticket on it, the seat chart shows no fewer than 15 seats open for selection, most of which are not MCE or "preferred" seats. So I have no idea why I cannot select seats, unless AA is now treating BA avios coach awards as "basic economy" inventory such that seat selection is off limits. Flight was booked a week ago and this condition has persisted ever since. Anyone have any ideas what's going on? Thanks.