Two more rides this weekend of 50 plus miles. On the first ride I experienced the mileage doubling. As has occurred in the past it doubled after a lengthy break where I "paused" the recording. It remained doubled on the dashboard for a while, and then changed to display the correct mileage after about 15 or 20 minutes.
When I uploaded these rides to the cyclo site, the mileage reported was consistent on the various screens. This was not the case previously.
The only change from previous rides was that I set the circumference manually as suggested in a post earlier in this thread.
So at this point, I'm sort of happy.