Without any explanation or warning saw seat reassigned to an even number aisle ( angled away from window). Complaints were dismissed as no seat is guaranteed only the cabin. Suspect Air Marshall but will never know.
What was particularly aggravating was UA did not even bother to send text / email saying the seat had been changed. Revenue fare and appears all of the empty seats in the cabin I saw a few days ago were filled presumably by upgrades. Should have booked 9D as recommended but who knows may have been bumped from there as well.
PS: Just got a message they are overbooked and looking for volunteers - place your bid for compensation to give up your seat. I have my boarding pass now and flying tonight so hope no more drama.