Same as Adrian on my case, running the TT for more than 15, never had that issue, has the engine drive washer eaten the spinner backplate? that happened to me once and discarded the backplate.

Sorry, but it looks like you are overnighting the nuts, unless your prop hub is worn as well as the spinner and the nut is reaching the end of the threads.

This ideas are based on the information you provided, maybe pictures of all the parts might help to figure this out.

Regards