I have found on occasion when driving long-ish distances in a variety of cars
(a) spare glasses - if left in the tray between front seats the main screws gradually unscrew themselves.
(b) cameras in a bag, in the passenger footwell, various small screws unscrew themselves.
Taught me always to carry a jeweller's type screwdriver set around with me.
It is quitye possible that there is some vibrational frequency that is damaging the watches somehow...