Abbreviated version: Got new phone, fixed problem.
Unabbreviated version: I used to have this issue and it drove me crazy. I was thinking it might be the bluetooth control module under the passenger seat, maybe the head unit, streaming issues when my phone would intermittently connect to Optimum WiFi hotspots as I'm driving along, blah blah blah. Then I finally got a new phone, and BOOM, the problem is gone. My phone at the time was a Moto X 1st gen and it started doing this in its 3rd year. Since upgrading to a Samsung Galaxy S7, I haven't had a problem. In the month before getting the new phone, I would use an AUX cable and that seemed to work as well (not that this fixed the BT). Although this was inconvenient with my phone that I normally mount by the A pillar as Navi. Anyway, figured it was worth mentioning to everyone else having this issue.