I was on the ORD-ZRH flight on Sunday. At the gate they announced that anyone who was connecting with United or had a mobile boarding pass needed to have their passports checked. A bochur who was connecting from Phoenix was also not going to be allowed to board for the same reason, but they let him on with the acceptance email from his Yeshiva. He approached me so his parents could email the letter to me (he only had a dumbphone), and when we showed the gate agent the email, she told me that I would need to stick with him as he would also need this letter for the next flight, though they didn't check in Zurich. Separately, the bochur who sat next to me on the Israel leg told me he had the same visa issue in JFK, and booked a separate return so he could board.