Paper tickets were so fast. Fold, press, beep, done.
App based tickets? Constant announcements (I'm talking 10 or more during boarding) to turn your brightness up. Despite that, I saw
1 - 25ish percent of people had dark screens, so the attendant had to take the phone, up the brightness, scan it, then hand it back.
2 - A number of screen with cracks or something (didn't get a good look) that required moving the QR code around to get it to scan.
3 - An alarming number of people who didn't bother to even unlock their phone, who then proceed to fumble with thumbing or face scanning, close whatever they were doing, then go into the app and find their ticket.
I'd say the boarding process took at minimum two to three times as long as they did with purely paper tickets.