I have the same issue after updating to 17.1.1 . I first thought that it was due to a certain app which triggered this, but that was not the case (in my situation).
The strange thing I experience, is that it looks like that the audio is put into a different mode in the car (e.g. something like speech mode) and doesn't turn back to regular audio mode. Even the radio sound does not work in my case. After many attempts (rebooting, connect, disconnect, etc), I found the following worked in my case:
When the audio is in silent mode, try to make a voice call to e.g. your voicemail box and hang-up. In my case this sets the audio in the right mode again and it all works. I have turned off all apps that could trigger going back to the silent mode, so this is not a long term solution, but for me it works for now.
Hope this helps anyone and hopefully Apple finds a fix for the issue!