NP. Let me clarify. They aren't wiped, but since all unchecked in seats become available to anyone at the 30 min cutoff, as soon as we "take control" of the flight, any seat assignments are lost and cane be re-allocated. This includes F seats. The people who are on the DM list for an upgrade are the beneficiaries of these seats, and often, they are the same people who are already confirmed in F, but at times, someone of higher status requests an upgrade that didn't have one pending before. If the "rightful owner" of the F seat doesn't utilize it by the time it becomes "community property" I allocate it to the "most qualified" candidate for the job. (Whoever is #1 on the DM list.)

(*) C) AIRPORT CHECK-IN TIME LIMITS – APPLICABLE TO/FROM ALL POINTS
IN THE U.S.A.
UA RESERVES THE RIGHT TO CANCEL THE RESERVED SPACE, ANY PREASSIGNED
SEAT AND THE ENTIRE ITINERARY OF ANY PASSENGER WHO FAILS TO CHECK-IN
AND RECEIVE A BOARDING PASS AT LEAST THIRTY (30) MINUTES PRIOR TO
SCHEDULED DEPARTURE AND BE AVAILABLE TO BOARD AT THE DESIGNATED BOARDING GATE AT LEAST TWENTY (20) MINUTES PRIOR TO SCHEDULED DEPARTURE
OF THE FLIGHT ON WHICH THE RESERVATION IS MADE.

So it doesn't cncl the reservation automatically, but as soon as we "release the unchecked in seats" at the 30 min window, it is effectually, no longer a valid reservation. Pending upgrades that are not confirmed transfer automatically to the UG list upon checkin.

In the "good ole days", waitlist processing stopped 24 hours before a flight, and there was never this problem, but in an effort to maximize inventory, somewhere in the past decade, the waitlist processing has been extended well into the checkin window. Two separate systems are competing for seats, the reservation (planning) system, and ACI (the operational seat map/DM) system. Heck, I have even taken VDB's off of a flight 15 min prior to current dptr (delayed flight, irrops, it was well after scheduled dptr) and a co-worker cncld the segment in their reservation when rebooking (not SOP)for a later flight. A guy on my BP5 list immediately got a page that he had been cleared, as that seat went back into inventory. I didn't have a seat...the VDB's seat was going to another confirmed person who was checked into his reservation on time. I had to tell the guy that unfortunately, the 30 min cutoff has passed, and any new reservation will not be honored. Obviously, he wasn't happy, requested a supervisor, and made me explain to the supe how the other agent had made a mistake, and that the waitlist clearance that never stops processing, even after ACI is in effect, had cleared him a reservation, even after the point when reservations have no weight. This is a known flaw in the system, but one that has too low of a priority for the gurus to fix.

Phil, there is no way for an agent to make you #1 on the list. He/she either added you, and your status/fare made you #1, or he/she took you out of order. The list sorting is 100% automation, while processing it is manual.