Today on my Acela trip WAS-->NYP, two different passengers near me had their tickets scanned and the conductor informed them that their ticket was "not registered" - they were told to call 1-800-USA-Rail or he wouldn't accept their ticket. Unfortunately I was unable to see if they were smartphones or paper e-tickets (sorry!)

One of them got pretty stressed at being told he had to make a phone call. I think he moved seat because after a while the conductor went through the car, re-checking everyone's tickets, trying to find him. Then there were several grumpy announcements calling for him by name. The final announcement threatened him with police at Philly if he didn't make himself known to the train staff... Seems he eventually turned up and got it sorted.