I have a Samsung Galaxy S6. When driving somewhere, I start navigating in Google Maps, and the route appears on the screen, but there are no audio (spoken) directions. Bizarrely, the only time anything is said is "you have arrived" once I reach my destination.
The problem isn't something obvious like audio being muted because when I play a test sound I do hear it. I have Android version 7.0 and Google Maps 9.69.1 installed.