I have MIA-ORD AA1185 fare A in First for July, 8th

Upon booking I've choosen seat 4E, now I've been placed to 3B (which is not the best seat in First).
That's fine, but now for my itinerary I don't see any seats available in First, but when I go to the seat map, I see 4, 5, 6 E and F available - 6 on total.

What's going on? Who 'grouped' those available seats together and why they aren't available to paid First and AA EXP passenger?

My only assumption is the aircraft change/upgrade from 738 to 757 or to 763.