Yes.. soooo… I´ve gone through sonos support, as always very helpful and real good service. They went through my setup and found it to be just grand. Then back to Samsung, which also gave superb service. Two hours on chat and phone. Did a HDMI reset on all ports and reseated the cables in the OneConnect, no effect. Did a factory reset from the menu on my tv, no effect. Then we did a “deep” factory reset initiated from remote support and there it was.. all ok. That is, until next full power cycle and the problem was back. So the next thing to do before Samsung escalated this issue to level 2 support, they asked me to test the Arc on another TV. As I started to disconnect the Arc I noticed the HDMI was just a little bit askew, barely visible… I´m quite embarrassed to say this, but reseating the HDMI on the Arc fixed the problem. Good grief.. the first thing I should have checked was the last thing I checked.
Lessons learned: No matter how competent and knowledgable I like to think I am… ALWAYS check the basics first…
Thanks to both Sonos and Samsung for their patience and service.