Since iPhone OS 11 update, music (audio) won't play over bluetooth in car

Since updating to OS 11, and subsequently to OS 11.2.6, on iPhone 7 Plus 256 GB Model MN4W2AA/A, I can't play music (audio) via bluetooth in 2015 Jeep Grand Cherokee. Before updating to OS 11 from OS 10.3.3, I had no problems with audio via bluetooth connection. Under OS 11.2.6, the paired iPhone works to make phone calls via bluetooth on the Jeep's UConnect; the UConnect shows the bluetooth for phone AND audio as connected and working, but the audio will not play in the car. I have tried various fixes recommended online and none have worked to fix this obvious bug in the OS 11 operating system:

1) unpair and "forget" the device in the UConnect and delete UConnect on iPhone in bluetooth settings. Turn off iPhone and car. Restart iPhone, restart car, pair the iPhone to UConnect again, still no audio.

2) in settings on iPhone, reset the network settings. restarted iPhone. unpaired and then paired from scratch the iPhone in the Jeep as outlined in #1 above. Still no audio.

3) went to my Jeep dealer, had them run software update on UConnect system in Jeep. Repeated steps in #1 above. Still no audio.

4) tried using USB cord to connect iPhone in Jeep. Still no audio.

5) tried to see if I could downgrade OS from OS 11 to OS 10.3.3. Read online Apple will not "sign" OS 10.3.3 so this cannot be done.

6) google searched this issue and saw hundreds of other people with this/similar bluetooth problems due to OS 11. No fix offered by Apple.

Question to Apple Support: can you tell me how to fix this issue? do you know if Apple engineers are working on this bug in OS 11? why can't Apple "sign" OS 10.3.3 to allow iPhone users to downgrade to until Apple provides a fix?

Community members: does anyone have a fix to this issue I have not tried above? thank you.