As soon as I checked in, it would prompt me to either photograph my ticket stub or tell it that I lost the stub. I don’t think the app would let me check into another movie until I did one of those two things, though I never really tried it.
A couple times early on I thought the app was freezing when trying to submit my ticket (before I learned the app just took forever to submit the photo—may have been a problem with my phone, not the app specifically, unsure). At least twice I remember telling it I “lost” the stub just to clear the prompt, then opening a support conversation, explaining the app wasn’t successfully uploading my photo, and then I could just take a photo with the regular camera app and attach that to the support conversation I had so they’d manually verify it.
Then I finally realized that if I really just waited for much longer than seems reasonable for the little progress spinner, eventually the photo capture in the app would eventually complete.