I printed a paper boarding pass when I arrived at the airport last week, even though I already have a boarding pass in my mobile app. The flight was delayed for an hour and half, during which time the boarding pass disappeared from my app. I couldn't even find my reservation for that flight in the app. It only showed my return flight as my next reservation.

Good thing I printed a paper boarding pass, but I also wonder whether that caused the mobile boarding pass to disappear from my app.