When I try to check in online for tomorrow's flight, I get:

"We can't check you in online, because you have a Special Service Request that requires you to check in at the airport.
Please see an agent at the airport to complete check-in.
You can always view your trip details at My Trips."

I get that both on a laptop and on my phone app. I called the DM line and they can't see any reason why that's the case. Any idea why? This is a return flight.