I was going to say Chinese ports don't accept mobile boarding passes. I had seem foreigners in Chengdu, a group of them, try to show the custom the mobile BP and all were turned back, and asked to go back to the counter to print out paper ones. A big argument happened, but they were eventually all turned back.

Oh, and they all just walked up to the custom as they all have no checked-in bags, looks like a group of backpack tourists.