So to close the loop, the initial warning message I saw was just the Delta website crash yesterday. But! This morning I woke up and got the notification that my seating chart was "view only." So I called in and they confirmed the upgrade did clear. But the ticket needed reissuing and it actually took about 40 minutes on the phone for them to sort it out. No idea why it was so hard, but they had no objection and got it done. So now seated up front for the flight to Puerto Rico.