I saved a screen shot of the tickets w/ bar code on my phone.
That meant I didn’t need paper but also did NOT need the app (in case internet was an issue). Just open your photo gallery and your ticket is always there.
The Hogwarts entry was no different than the park entrance scanner.
Having said all that, the ticket scanning at Universal if a terrible inconvenient joke. Invariably, someone‘s ticket won’t scan or their finger print won’t work, people need to activate tickets, or, or or...
I tried this method myself and couldn't get the scanner to read... ...Not sure why it doesn't work, maybe protection against someone from taking a pic of ur bar code but we ended up having to manually type in the serial numbers...