Holy Crap! This happened to me yesterday!!! I was flying from Stansted UK to Valencia Spain. I got there about 1.5 hours before having checked in online. The kiosk wouldnt let me print it out and the mobile app didnt work. I had to pay 15 pounds to get a printed ticket. There was no physical way to board my plane without paying them money!
Never again. I wrote an email to my entire company forbidding anyone to use Ryanair for travel. Going forward all expenses submitted on Ryanair will be denied. We are not a huge company, but with offices in the UK and Spain, we used them fairly frequently.