Originally Posted by redwoman

This happens when UA can't seem to confirm the equipment for a flight, so they leave it hanging. They allow tickets to be sold, but no seats can be assigned until they figure out what equipment will be used. You can't even call Reservations and ask them to assign seats, because they can't see a seatmap either.

It's not really a blow-off on UA's part, though I share your frustration at not being able to choose seats on your last leg and wrap up your trip plan. This happened to me for an itin that i planned almost one month ago. The seatmap for the 4th and last segment of an itin was unavailable for almost a month. It made it a nail-biter for me because the pax in question were a dad and 3-year-old. Imagine the mess if they were not able to sit next to one another.

Just remember that if you can't assign seats, nobody else can either. Keep checking each day until the seatmap opens up, then grab a good one.