Same problems. Award ticket and seat assignments gone
We, too are dealing with on again off again tickets and seats as our HNL-SFO flight was switched from UA to CO.
1. Award ticket (60,000 RDM spent) disappeared with zero notice.
2. Seat assignment for paid passenger disappeared.
3. Upgrades gone with E+ not even an option.
4. Just completed 5th call (over 2 weeks) to United for corrections. Agent says she "called Continental and confirmed seating". I've heard that all was fine after each call, but glitches remain.