One thing that will affect the clamping pressure on a wood prop, e.g.,
torque value on the bolts, is a change in humidity. Even after the torque
settings have settled down, a significant change in humidity, whether at
your location or due to traveling to an area where it is different on
average, (coastal area to desert or vice versa, for instance) you would be
advised to re-check your prop bolt torque.

Dan Schaefer