Available Seat Not Showing on Up Sell But Does for New Booking
 

I know a similar topic was recently covered ad nauseam but this seems different than what I was experiencing AND I just spent too much time looking for it so forgive the dupe if it is... And, thank you in advance for those who will point out my ignorance and lack of search ability.

I have ATLMSP booked for tomorrow in Comfort + and the app and website keep offering to up sell me to 1st for far too much money to even consider. However, when looking at seat map, there are none showing available. Separately, I went to see what might be available (any cabin) on earlier flights for same day change. I noticed they were still selling 1st class seats on my flight so I checked the map and 2 seats were showing available.

In the previous thread, it seemed they "fixed" or changed the part about not being able to see available seats in other cabins so I find this curious.

It could be that the seats are blocked for Gate Agent assignment. It's a bit rare in F, much more common in M.

Fixed?

Not for me, unless there are no FC seats on any of my future flights

Not sure which thread you're talking about, but as of now cabins other than the one you're in are consistently blocked on existing reservations.

This had happened for a while, and then was "fixed" and went away, but then it started again a few weeks ago and at least so far has not shown any signs of disappearing again.