Sometimes Bluetooth does not activate properly. My radio is the one with navigation. My phone is an iPhone 6S. This is very intermittent. Perhaps once every 20 times I drive the car. If I go to the device settings on the infotainment screen, scroll down to my phone, then press audio and phone it comes back with the message that the phone is not connected. If I press Retry it fails.

When I look at the Bluetooth menu on my phone the Mazda link is not connected. I have deleted the link on the phone and gone back into the car menu and deleted the phone from the list and have pressed Add a New Device. The Mazda Bluetooth signal is not visible on the phone.

I have stopped the car and restarted it without success. After arriving at my destination, going about my business and returning to the car I able to get things working again without difficulty. The problem then returns a week or two later.

I never have any problem with Bluetooth on my 2019 Subaru or my previous two cars and I never have any problem with Bluetooth on various rental cars when I travel. So I am 100% certain that the problem is not in my iPhone.

UPDATE
Went to the dealer today (12/3/19). They installed an updated operating system. We'll see if that solves the Bluetooth connection problem.