This is a domestic flight - so very different upgrade process.
If you requested some time ago, then the domestic upgrade is waiting on U class availability - and will clear when (2 in your case) U fare buckets are released. If the load factors are even reasonable in J, then the U seats (allowing anyone to book with points) are unlikely to be released.
The declined at T-6 would appear to be the final clean up because no U seats are being released.
If you had then requested an on-departure upgrade in the lounge, then things might have been very different. These get processed after close of checkin, and may fill those remaining seats (probably with catering not assured).
This is very different to the (farily new) International upgrade process, which works right up to departure on the original request (but AFAIK does not rely on or look at all at the U bucket released).
All this assumes that you did not request upgrades (again) in the lounge after check in.