Do I understand correctly that one of the connectors under the seat is
actually pulling apart?  They should lock together securely and shouldn't
be able to come apart unless something releases the lock mechanism.
Moving the seat shouldn't be able to pull it apart.  If it does, there's
some sort of problem that needs to be corrected, such as insufficient free
length in the wire harness or an ineffective locking tab.

Have an '04 XG350L and this issue has occurred three (3) times. First time
was a bit worried and had it immediately checked at dealership. Caused by
me sliding maps, cloths, etc. under my driver seat, as I've traditionally
done in all my cars.

Second time, figured it was something under the seat. However, nothing was
there, or had been! Brought it into dealership, fixed in 20 mins.
Technician (who was great) noted that one of wires in the underseat harness
had come loose.

Third time it occurred- had some groceries in the back seat well and some
items (Cans, etc.) rolled under front seat- sure enough Dash indicator came
on. Simply cleared under seat and pressed on harness items and top of seat;
started car and indicator was off and has remained off. Next time I'm in
for an oil change will have dealership check it out again.

From your incident and mine, it appears that the Airbag sensor component
and/or wiring harness definitely needs some post-install "tweaks" or
re-engineering.

Regards,
Robert G. Ragosta