I noticed this issue this morning when my Google Maps navigation was silent, and so I missed a turning, and I proceeded to diagnose the root cause when I got home, and I end up associating it to Spotify.

I use Spotify and Google maps almost every day when I am driving with no issues at all, phoned paired through BT and there is no issue. However this morning, the voice was silent, Spotify dimmed the music, but no voice was heard.

However if I kill Spotify (force stop in settings) and then test the audio, the voice plays perfectly fine.

Weirdly this problem only exists over Bluetooth. If I am disconnected from Bluetooth Spotify dims the music and the voice plays. However if I am connected to Bluetooth with Spotify playing, and tell google maps not to use Bluetooth for voice (so play out of the phone speaker), it is still silent.

This has to be an update from Spotify somehow causing this, however this worked perfectly fine for me just the other day