Closing out these items took varying amounts of effort from checking the inspection reports to rallying test engineers to instrument motors with strain gauges and run a sweep of tests. Working with our structural engineering team we root caused this issues to a mismatch in FEA to reality. It also highlighted our testing at the component level wasn't doing a good job accelerating this kind of failure. 

By iterating through different geometries that added stiffness, minimized weight, and maximized manufacturablity, using NX and FEMAP, we were able to bring peak stresses down to a region where we could achieve our life targets. Calculated using the fatigue strength of our material and the cyclic loading condition.

Finally to verify and validate the solution the part, motor, and aircraft must pass a series of tests. Work is ongoing to develop a test setup at the part level to validate this change which will allow for the fastest iteration loop.