I had exactly the same problem. Updated IOS and then got Iphone7. The 7 worked for a week or so and then the same dropout problem came back. Deleted the connection fro the phone and the car. Now have a new problem. The phone works perfectly via bluetooth for phone calls, but nothing for streaming music at all....
Paired a friends Samsung S7 and that shows on each Bluetooth connection if it is phone and/or music. Stated only phone, so same problem with the S7 as well.
I have no idea how to get it going or if it is possible, however I do find it odd that I have the same problem with both phones when the problem didn't exist until a few weeks ago and my friend has not updated the last Samsung update.
Sorry I can't help, but would love someone to find somewhere in the car to turn the damn music streaming on.