They have no idea why it happens. They come up with the stupid excuses in tech support. I have and use two legal US passports in the same name. Both are in the Customs and Immigration system and in the United IT system but if I use one for one trip then try to use the other for another trip OLCI always fails. I can't toggle between passports. It remembers only one. If there is some other secret reason for this (which I don't other than physical verification of the passport (a Continental thing) we should be told it is there. If we are randomly selected in advance then we should not be invited at the 24 hour mark by email and phone to check in online only to find out after the form filling that it doesn't work. This is something that came with the radioactive merger. The UAL system worked fine. I think it has to do with passport verification and the program's inability to toggle between different travel documents. What I do know is that this crowd does not give a hoot about informing us or fixing the problem. They treat us like so many lab rats running through their mazes in search of increasingly elusive rewards. New United boils down to they don't care.