Another data point FWIW
Curiously, this issue is also affecting Citi card-owners down here in Argentina as well. Upgraded my Gold AAdvantage Visa to Platinum in Dec and got a Plat MC as well. Both have different issues. One started reporting "Incorrect AAdvantage number, contact customer service" on the website, but says nothing except "0 miles earned" in the paper statement. While the MC reported an incorrect AAdvantage number (9999999), but the miles earned number was correct. Neither reported any miles to AA.
After asking AA to check, they found my MC had another AA number assigned. They deleted that one and assigned the correct one. They found nothing wrong on the Visa card. Yet the Citi website stayed the same for both.
Until today. Both cards are now showing up as "AAdvantage number not yet confirmed". So this looks like it's not only AA's problem but Citi's too.