I had the exact same thing happen. I had a business elite seat -- free reserved and redeemed for my wife. Me and my son had redeemed for coach round-trip. The return did not clear from BCN to ATL for my wife's business class seat. I am PM, and it was odd that only my wife's seat cleared on the outbound.

Anyway, the night before ... (back in June)... there were about 15 open seats on the seatmap. But the waitlist did not clear.

When I checked-in... I inquired about my wife's seat. The check-in agent said that it did not clear and there was nothing that could be done. I expressed (politely) that I was disappointed to have already redeemed all of the points. I felt that I had already "paid" for a business elite seat for my wife. I told her that I was a bit embarrassed for not being able to get my wife up front. I asked to speak to a supervisor. I went over to the "booking" desk and spoke with an agent there. She said cited the 24 hour rule and that there was nothing that could be done. She admitted to the person in front of me that there were no coach seats, but that there were business class seats on the flight.

She said that she would see what she could do and that if there were any opennings, she would give us a seat at the gate. My original thought was that she was just "getting rid of me". I presumed that they would be able to fill the front with non-revs... and we would be out of luck.

At the gate, to my surprise, they called my wife's name. She was given 6C!

About 15 minutes later, and to my total suprise... (after hearing a lecture earlier on how valuable DL's business elite product was...) my name and my 4 year old son's name was called. I approached the desk... Our award coach seats were exchanged for seats 6A and 6B! OP upgrades to anyone who was Platinum and their travelling companions!

Anyway... I am not sure why they do not seem to clear waitlists for that flight back from BCN to Atlanta.