I once studied Bluetooth in depth considering buying a license for a product I was developing. At the time the better implementations wanted 500k of ROM for code. Others wanted more. We decided against Bluetooth. Never regretted.
My conclusion then was that Bluetooth is a mess. Nothing I have seen since to change my mind.
There is a stacking order of connections which is supposed to magically assign the desired priority as to what overrides what. It never seems to work when more than 1 phone and 1 headset is involved.
I second pcmem's suggestion that one start with a factory reset. Then note the order of pairing phone, GPS, whathaveyou. If that doesn't work well start over and pair items in a different order.
Sena headsets were notorious for requiring a factory reset between firmware revisions. After update not even factory resets could make my two 30K's behave the same. Cardo Packtalk Bold has been much more reliable but still powers up Bluetooth differently every time I ride.
2018 F-150 XLT SuperCab 4x4 2.7L
2016 Beta 430 RS
2016 Subaru Outback
2013 Tesla Model S 85
2009 Husaberg FE450
1983 Porsche 928S