Hi,
Here this happened almost always with more recent versions of the firmware. I'm now using version 1458053248 and use "dtparam=audio=on" in config.txt, and the problem seems to be gone.
Google comes up with nothing even close for "1458053248". From where can I get this? I see a place like this:
https://github.com/Hexxeh/rpi-firmware/commits/master/bcm2710-rpi-3-b.dtbBut I have no idea from where official firmware comes from, or where it's stored...
Thanks, John