Adding my experience on 4/1 on JFK-MIA on a 777 with Flagship Business. In the recent past I've been clearing this at T-48, since it's so J heavy. However the buy up offer on app was only $161 and likely enticing for many.

At T-24 there were only J2 seats visible on seatmap. On the upgrade list me and my non-elite companion were #6 and #7 out of maybe 15 or so. At T-40, #1 and #4 cleared. #2-3 were same name so likely linked and didn't clear for the one remaining seat.

​​​​​​Once on board, #5 was moved up by gate agent just before the door closed. Then we had a 3 hr delay on tarmac (if you followed this weekend's Florida shenanigans) before returning to gate, where a handful deplaned, including 1 J passenger. 30 mins later we're ready to go and the gate agent appeared to upgrade one of either me and my non-elite companion.

I still don't know why the couple/family in #2-3 weren't upgraded at any point, unless the GA asked and they didn't want to split up. My companion enjoyed a nice 3 hours in J.