I take screen shots all the time...that is digital backup 101. There are a zillion reasons...email does not connect, Apple Wallet closes too soon, sync issues with opening App...the glitches always seem to happen right when you need it most where you can easily recall a saved screenshot and keep it open on your device to scan.

Heck, I even had one flight where we were delayed significantly but the "system" did not update so the app presumed everyone boarded. Once we actually boarded anyone that was trying to use the mobile app no longer could recall the boarding pass and had to go to the counter to get a paper boarding pass as everyone else was walking on. It was a cluster...meanwhile my screenshot saved in photos scanned me right in.