I've run into the same thing. For Hulk and other rides with mandatory lockers, I usually screenshot the Express pass beforehand so it's ready on my lock screen. Haven’t had issues with team members scanning it that way. Still, printing it like you mentioned seems like a solid backup, especially if your phone ends up locked away or the battery dies. It would be great if they added scanners outside the locker areas or linked Express directly to your park ticket for convenience.