Thanks for adding me to the beta program! Opening the TestFlight app I can't see anything to test? There is a Redeem button in the top left. I don't have a code to redeem and the email I did get doesn't any any TestFlight info?
I've been getting the same issue and so has my partner on her phone. Closing the app and re-opening it seemed to help a bit. When it comes up with the Touch ID we click "Cancel" and the put in the master password, this got the passwords to show for us. But we're still getting sync issues: To get it to do that sync I had to change it from using Dropbox to Google Drive, but still getting the same issue. I am also using v. 5.5.4 on iOS 11 beta. I believe I was getting the same issue on iOS 10.