Good afternoon. My current firmware, which I installed "BV8000Pro-Blackview-V0.1_2017083_20180105-1104". For three months of different reinstallations and following your instructions I report: using Bluetooth of my car to play music, a call, interruptions occurred every 3-5 minutes, after 20-30 seconds the connection was restored periodically and again disappeared. I noticed that the car completely lost the "BV8000Pro-Blackview" and wrote that I do not have a number of "Bluetooth" devices.
Firmware 20180105 is old and carried a bug on the Background task clear setting wich makes the fix posted in this thread not working as expected.
Please update (flash) your device to the latest firmware (20180308), perform a factory reset, apply the fix posted in this thread and report back