BMW Bluetooth Connectivity

I have an iPhone 11 and Bluetooth periodically disconnects during phone calls, then reconnects automatically. iOS 13.5.1 and BMW's update website (www.bmw.com/update) says my vehicle software is up to date. Very annoying. 2018 BMW 640GT. There's an old thread on this, but it's about a year old. Been going on for some time, so it predates the current iOS version. Apple Car Play works fine during calls (it uses WiFi), but my preference is to use BMW's in vehicle NAV and Entertainment option. Anyone else with this issue? Or is it the BMW Connected App causing it still?