I have this issue too and I am using an aftermarket Pioneer AVH-X8500BHS head unit. However if I'm listening to Bluetooth audio, the audio will go quiet for a second as if a notification came in, but no notification will go through the speaker system and the phone won't make noise either. It's quite annoying cause then I have to look the phone to see what it was. I also have the same issue when using Motorola assist where it will understand the command but I can't hear the response.
Is it possible to set something up in Tasker to be able to play the sound through the phone speaker while still retaining Bluetooth connectivity for music?
I have also tried tinkering with the Bluetooth settings in the new assist that gets upgraded and 4.4.2, but to no avail.
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