FORUM RULES UPDATED - The forum rules have been updated to continue to provide a friendly and safe environment for our member community. Please take a moment to review the updated rules and our terms of use and privacy policy. Click here for Forum Rules which has links to the 'terms of use' and 'privacy policy'.
It may be the bushing inside the prop which takes the place of a shear pin and can slip when worn at high speed
Mark a straight line on the inner bushing with the outside of the prop, if they move out of line that then would seem the cause of your problem