I do not think it is a document problem. We're both US passport holders, both enrolled in GOES, and even occasionally get Pre-Check. It seems to be a problem with UA not remembering that they saw the same person with the same US passport that expires in 2021 ten months ago. I didn't try to check myself in since that might screw up getting seated together on the SN leg, so I don't know if it would have completed the transaction.

I had roughly the same experience when departing for Brazil a month ago, traveling solo, so I should know better.

It is reassuring that we can get decent seats on SN. It's a 319 that seems to be sold out at this point. Thanks.