Flew in November with my wife on United tickets with Eurowings segments (1 paid ticket, 1 award). When we booked the ticket in April, it actually showed two different Eurowings booking codes (on each ticket), next to the United booking code (did not copy those numbers for my ticket, I did for my wife).Later one of the two Eurowings numbers disappeared (was the case for both tickets) and the remaining number did not work. First flight of the tickets was on Eurowings, so I could not check in online, as I only had the non working confirmation number, while my wife could check in. Checking in at the airport was no problem.