I had a BA Avios booking on an Aer Lingus flight to/from BCN last week.
We intended to check-in our cabin-sized wheelie bags because we had a couple of liquids more than 100ml. This would have been under our 23kg checked allowance.
We went to the self-service kiosks for check-in and bag drop. We selected "1 checked bag" while checking in and managed to print our boarding passes. The kiosks then wouldn't let us print bag tags. I can't remember the exact error message but it was something along the lines of "cannot retrieve baggage allowance information for the booking". Of course, the staff member assisting people at the kiosks couldn't actually assist us and directed us to the staffed check-in desks. There was an insane queue for the desks so we begrudgingly binned our liquids that were more than 100ml and headed for security with our wheelie bags. Our boarding passes from the self-service kiosk did say that we could bring a carry-on and there were no issues after that.

Unnecessarily frustrating - their IT systems are a mess which in turn creates a massive queue for the staffed desks. It should be seamless!