I'm using latest versions of iOS and Google Maps on an iPhone 7, and when I turn the screen off, I do not hear turn-by-turn directions when using the navigation feature of Google Maps. Yet, according to the "Battery saving tips" of the Google Maps app documentation, I should still hear the sounds.
I verified this by turning off the screen (pushing power button) a few seconds before the next turn navigation came up. Then verified it was working by leaving the screen on for the next turn. The phone is not connected to any bluetooth devices either.
Also, the Google Maps settings all seem to indicate that sounds are all enabled properly (volume icon on map is set to "unmuted"; under navigation settings, all relevant-looking settings are enabled; etc.).
Any ideas why this would not be working for me? I've yet to try a restart of phone nor have I tried a reset of phone. (Will eventually try those if no other suggestions come up.)
Update: I also just tried re-navigating to new location; I turned screen off in the middle of the, "okay navigation all set" message. Then, the "you're on the fastest route" message played while screen off, but then all the directions no longer play, so issue still happening.
Update 2: I disabled bluetooth and restarted the phone, and the problem still exists. The voice directions also do not play when I have a different app in focus. I'll try a fresh install of Google Maps at some point soon.