Well .... I was replying to the post just ahead of mine (how can you tell the cabin is oversold), not your OP.

From your OP, I don't know any exact sequence of events, so can't really come up with a solid theory.
You claimed that (on the app) having an MVP upgrade box checked, excludes the 7:20p flight from the display. I can only assume that without this box checked, you did see the flight. What I don't know is which search (MVP checked vs not checked) came 1st nor how far apart the entries were. I will say again that Yield Management allocations are dynamic. I feel a lot of FT'ers think that an airline decides allocations at the time a given flight is opened for sale and that those allocations are static until the flight departs. This is nowhere close to true.

From your viewpoint, checking/unchecking this MVP box is what changed the availability of 2 coach seats @ $279 each. But did you go back-n-forth multiple times to verify this theory ?
Many other things happened between your requests. Some possibilities have already been mentioned by other members. So I'll add that dynamic re-allocation may have also happened.

Bottom line: "time" happened.
AS uses Sabre as the core to their reservation system. While I have a background with Sabre: 1) my expertise is on the Flight Operations side 2) I have no familiarity with the AS contract ..ref do they use Sabre Yield Management vs having their own.
These airline Res systems are all real-time and in most cases (Southwest is an exception) talk to each other practically real-time. And most travel agents & websites are tied to these systems for actual bookings. If you think that worldwide, you were the only person "shopping" for these flights at the same time, you are seriously mistaken.

Getting back to your thought that the MVP box makes a difference, I read thru the thread to try and decipher it.
Screen shots by RAD_PDX seem to support your theory ... but if I'm reading them correctly, the findings are opposite from yours (and in line with your thought that MVPs should get "better" search results than the general public)