Several owners have reported broken tailplane struts with a fracture point at the lower threads.
It's a good place to cast a vigilant eye over during the walk-around. Some builders have reversed the threads such that the female is welded into the lower strut.
A number of builders have also reported broken tailplane bracing wires. It is thought that the wires may be weakened by vibration. This could potentially be affecting the lower struts as well.
Early in the life of my aircraft I had a friend take a look for any vibration during formation flying, not seeing any. If any were apparent, placing a camera to observe closely would be one idea.