Thanks for reporting this marantz. I'm another nuc user. I see on the libcec github pages that opdenkamp has found a possible cause in libcec and is going to fix it. ![smile :)](https://forum.libreelec.tv/core/images/smilies/emojione/263a.png)
I have a slightly different issue but I suspect the cause is the same. In my case, since upgrading to 009 cec has gone a bit wacky, e.g. switching my amp to the wrong input, assigning devices to the wrong parent - all quite weird. I was able to mitigate it to some degree by manually assigning the correct physical address but the problem tends to come back. Rolling back to 008 and all is good again.
It would be great to get the updated libcec (when it's done!) rolled into the following LE build.