As far as the earlier seat change, this has affected others. Here is UA Insider's statement on this, found here:
http://www.flyertalk.com/forum/18114732-post1.html
Seats
Sporadic Seat Assignment Issues. We continue to see sporadic cases where some pre-assigned seats were lost. We’re working on a process to automatically assign seats back in these cases, but, there may be times when the originally assigned seat is no longer available. We recommend using united.com to confirm or change your seat assignments for any upcoming trips.