I am getting this message when trying to check in for a trip tomorrow.
"Unable to Complete Check-in
Check-in has been restricted to the gate. Airport check-in is required."

1K desk was of no help. According to them, web support says it is because I have a 6 hour layover.

Added: I was trying on the app, which gives the above message. Interestingly, when I look on the website, my reservation doesn't have the "check in" button on the reservation.