I can con confirm that the iOS 13.3.1 does NOT fix the issue. No sound for phone calls or Siri continues to be an intermittent/random problem with my 11pro and 2019 Subaru Crosstrek. I have tried every single “fix” on this forum. Just sent the USB C adapter and cable back because it didn’t help. I can be talking on the phone one min and the next phone call will not have any sound (it connects, but no sound).
i have made 4 reports directly to Apple.
I think this is a safety issue.
I wish for someone to propose a fix that actually has lasted over one month, otherwise I will personally not consider it a fix. Ive gone as long as three weeks with no issues. Then, BAM!