Ryanair are still having problems with the app.
Its fine on outbound journey, but when you try to check in for return journey it dosnt recognise the booking??
Dont log, just enter as a guest, that way you should then see your boarding cards (still a bit of hit and miss)
One day they will get it right but probably just want a little extra money off irate passengers at the airport to pay for further upgrades of app!!
Take a picture of the boarding passes on your phone incase the app goes down, i used these with no problem.
See reply from email I sent to Ryanair regarding this. hope it helps
Dear Customer,
Thank you for contacting Ryanair.
Regarding your correspondence, I inform you that, if a customer booked their flights using My Ryanair account they will be only able to view/check in/download their boarding cards on Ryanair App once they log in to My Ryanair account. If the flights were booked not using My Ryanair account then customer will be only able to view/check in/download their boarding cards on Ryanair App when they are using the app as a GUEST.