Buonasera Umberto,
same error here with FSLabs A321. Having selected the gate as usual upon arrival (already on ground), then when arrived at the selected gate after the message to cut engines, I, as usual, turn off beacon and then seatbelts and GSX instead start deboarding process crashes with the couatl error reported above.
I attach the couatl.err file that probably contains useful informations for you.
Grazie,
Federico