I've had similar experience...and have noticed several other threads here mentioning the same.

Last month, I made a same day booking and assumed that was the reason the seat map was grayed out. We ended up in great MCE seats at checkin.

Yesterday I helped a friend who is silver make a booking that is more than a month out and see the same grayed out map with preassigned seats in the last row. I tried calling AA on his behalf, but decided to wait until the current disruption clears, as this issue is not pressing.