It has happened to me too although you'll be fine. I had a booking that was involuntarily exchanged due to a schedule change, and after that happened, it would never show me the seat map. Even after I did another change (weather waiver) the seat map would not appear for me "This itinerary is not eligible for seat selection. Please call 1-800-JETBLUE for assistance"

The seat map should work fine at OLCI and at the kiosk if your departing airport has them.

Flights posted no problem.