Just happened to me. Everything was working fine, got to destination and shut down car (pressed start/stop twice). Came back to car about 30 mins later and no audio
Thought it was a pairing issue then it dawned on me this was the issue described here.
Got to another destination and tried restarting the car and turning audio on and off, powering up the car, shutting down, nothing. I took a video to show my SA when I bring it in and gave up. I knew it would come on again, probably in the morning or when I drove it again the next time. A few minutes later while still in the car, I heard a faint pop or snap, like an amp shorting. I knew that was it. Turned the car on and radio came on immediately.
Pretty sure it's the amp now. Does it affect HK models too or is it only confined to the base units?
Edit: it was in the mid 50s here today so I don't think this issue is cold related.