The one time I tried using a mobile BP rather than stopping and printing one at the kiosk (because I was unusually behind schedule, and needed to catch my plane), when I got to TSA, exactly the same thing as depicted above happened to me. Nada shown. It cemented my view of needing to have paper BPs, every single time.

But what also drives me batty is that the UI to the United app is continually changing, contributing to how often it is stunningly challenging to get it to do what I want, including displaying a BP. From an equivalent standing start, I can have a paper BP in my sight in about 3-4 seconds (bend down, open my briefcase, pull out my travel wallet, unzip and fold it open), and it always takes substantially longer to do the same to get to an electronic BP on my phone (bend down, open my briefcase, pull out my phone, unlock it, swipe to find if I have the UA app open, start it if I don't, wait for it to maybe find a network, maybe need to log in, fiddle around to see where they put BP access with this version, maybe need to refresh the info; if I want something other than the current leg's BP, fiddle a ton more to figure out where that is, etc). I recognize that some people prefer using their phone, but not me.