I am also having the exact same problem with the Pixel3ROM rom which is quite odd since that runs Android 10.
Im having the bluetooth drop out issue playing audio to my car stereo. Did anyone find a fix? I saw some say updating fixed it for them, but Im already on the latest version (PixelExperience_polaris-9.0-20190914-1129-OFFICIAL.zip).
Other than this the ROM works flawlessly, but this is really a show stopper for me!