I have the same issue with driver side 3rd row. Happened once before while under warranty and dealer said they had to reprogram the ECM to recognize/relearn the 3rd row seat. There was never anything stuck in the tracks/gears or blockage under the seat, and no motor failure either; ECM just forgot what to do when the button was pushed?? It tried to lower, about 4 inches, then returned to the full upright position. My guess is that one of the two motors is not getting the signal to operate?, causing the momentary operation down, then back to upright. I will most likely have to take it to the dealer again, this time out of warranty :-(
9/12/2023 UPDATE:
I was able to get my 3rd row seat (driver side) to work again. I ended up using the recline button (on driver side rear pillar between 2nd and 3rd row seats) to rock the seat back and forth several times, the last time, I left the seat in the forward most position (there are three positions the seat can position to with this button, forward-normal-reclined); from there, I went to the rear of the vehicle and operated the fold-down button and it finally went down completely. I cycled the seat several times after that, from the rear of the vehicle, with no problems. I hope this helps others who are suffering with the same issue.