Friends are flying from CUN to FWA via DFW.
Return flight DFW -> FWA was AA #2989 on 10/15/21
Got an expertflyer notification yesterday that the flight #/route was changed (2989 now goes somewhere else)
Got the confirmation # and went online today and now it shows it's flight #2956 from DFW to FWA on 10/15/21 (only a 15 minute change)
However, it says "choose seats" and all their other segments have assigned economy seats.
You click the Choose Seats and the entire plane is X'd out and it says:

Please check back or we’ll assign seats at the airport. We’ll try to assign seats together, but if availability is limited, your party may be seated apart.

I'm not sure what the original aircraft type was, the new one is a CRJ-700.
Is it possible they downgauged the aircraft to a smaller one and now they cant' fit everyone on?
Just seems odd that all seats are blocked and they did not book basic economy (as their other flights have seat assignments)?
Or do I tell her to suffer the 4+ hour phone wait to find out what's going on?