There are no 3-class A321s operating on any route to/from CLT. They only show up regularly on JFK-LAX/SFO.

However, I booked a flight from CLT-LAX-CLT in June, and noticed that one mid-day departure form CLT is scheduled on an LAA A321B in the 24XX flight number range (aircraft has sharklets with power and AVOD, and Y begins in row 8). This has always been an LUS route utilizing LUS Airbus equipment, so this is a nice change. There are some rows of MCE on that plane, so it could be that Seat Guru is counting that toward some 3-class availability. In any case, Seat Guru is not known for reliable information so it most likely is a mistake - and no true 3-class planes operate on CLT-LAX.