Navigation reboot solution

We own a 2015 Prius V that I've lovingly named "Sparky". My wife and I upgraded our iPhones from 5c's to 8's late last year. I had some difficulty pairing the new phones to the car, but after a couple of tries we got things working. Every so often I noticed that my phone would not appear so I'd have to go into the phone setting and give Sparky some encouragement.

However, when we started on a major road trip and used the navigation we found that after a couple of hours (or just before a major highway turnoff) the system would reboot and we'd have to re-enter the destination. We also noticed that Sparky's spoken commands would sometimes be cut off--an indication to us that she was unhappy with something.

Someone on PriusChat suggested to completely delete the old pairings and then re-pair the new phones, which I did, but after a day's drive the navigation would reboot as before.

I looked again at the Bluetooth settings screen and noticed an option to reset the Bluetooth settings to the factory defaults. I did that, re-paired the phones and--happy day--Sparky's navigation system worked for the last day of driving without so much as a hiccup.

Case closed--by employing the Bluetooth reset option.