phone book sync stuck "refreshing"

I have a 2013 Prius II and an iPhone 6S.

I'm having trouble getting the phone book to sync.
Bluetooth is paired (music and phone calls work through the car).
The Bluetooth settings for the car have Sync Contacts on, All Contacts checked.
(I've tried it with the Show Notifications both on and off, but neither choice shows different behavior.)
And I've tried forgetting the bluetooth device from both the phone side and the car side, and starting fresh, and that's not working either.
I've tried turning both devices off and on again.
I have less than 300 contacts, and the manual states a maximum of 1000.

The Prius touch-screen just displays "Refreshing" but doesn't actually complete; I've waited several times, up to 20 minutes. I'd guess it shouldn't take longer than a few seconds -- it's a tiny amount of data for bluetooth rates.

Any suggestions? Is there a way to do an NVRAM reset on the entertainment computer?

 

Here's how you factory reset the 2013 Prius audio system computer:

0) Maybe take photos of your radio station settings.
1) press the Setup (physical) button
2) press General.
3) scroll down and press Volume Settings
4) press Navigation Prompt Volume.
5) Now touch the screen six times: first touch just underneath the back arrow, then touch the bottom right corner, then repeat that sequence three more times. A hidden menu will appear.
6) In the hidden menu, press General.
7) press Down
8) press "Set Factory Defaults & Reset Nav Calibr"

The system will reboot.