The music still plays just fine, but the car's display no longer updates with the song info (meta data). It will display the first song played, and then get stuck on that as subsequent songs come up. If I stop and restart the music player app on my phone, it sends the meta data for the current song...and gets stuck again. If I use the car's controls to restart a song, it refreshes the meta data...and then gets stuck again. If I exit Bluetooth, go to radio, then go back to Bluetooth, it refreshes...and gets stuck again.
Most of the complaints that I found about this involve streaming from Pandora, which I do not use. The best explanation I found was this:
I got as far as enabling developer options successfully, but I do not have an option for Bluetooth AVRCP Version.[SOLVED] The issue is your AVRCP version. Most likely you will need to downgrade it. First, you'll need developer options enabled on your Android (Settings>About Phone> then tap Build Number 7 times). After developer options are enabled, go to Settings>System>Developer Options>Bluetooth AVRCP Version. Try changing AVRCP version, restart the phone, and see if this fixes your problem. AVRCP is what controls the metadata that is sent to your bluetooth device.
I also found instructions to reset my infotainment center to its factory defaults, but I haven't tried that yet as I suspect that the phone is to blame, and I'm leery of screwing things up worse.
I don't have another phone that I can try in my car, nor do I have another car that I can use with my phone (I could hypothetically install a music player and some MP3s on Wife's S9, pair it with my car, and see if it has the same problem, but I'd rather avoid that time and inconvenience if somebody has a better idea.)
I did install a new app at about the time this started. An employer requires me to use Duo Mobile for their 2-factor authentication. Removing that app is not an option, but it's my primary suspect since it's the only thing I've changed recently. I'm unaware of any updates to Android (the last one listed is Jan. 2017), and I'm pretty sure my car's software can't be updated without a technician visit. I did restart the phone.
How can I pinpoint the fault? Duo app, music player, phone, or car?
Because all of my thousands of songs came from the annual SxSW downloads, I don't know their titles or artists, and rely on that display in my car to know what I'm listening to. This new bug is bugging me. Getting a new phone is not an option until Wife pays off her S9 in 15 months.