This has been a problem for me for months as an Android user. Clearing the app cache, clearing all stored app data and logging into the app again from scratch, and/or uninstalling and then reinstalling the app completely does not resolve the issue.
Bookings will appear as they should, then disappear a few minutes later, then reappear again some time later, all apparently at random.
Have checked in for flights on the way to the airport, only to have the booking and boarding pass disappear from the app by the time I get to the lounge. I have asked the lounge staff for a paper boarding pass (which they can easily print by scanning in my FF number from the app), but by the time I get to the gate the booking has reappeared again. It's baffling and low-key frustrating.