Folks having the problem may want to file a complaint with the NHTSA.
https://www-odi.nhtsa.dot.gov/VehicleComplaint/
Thor may not do anything until a NHTSA investigation is complete.
Although I have not had an issue in the rain, this weekend I will pull my arms and look at the splines on the adapters to see if there is unusual wear. I have a trip planned for Memorial Day and don't need any problems that can be prevented.