Thought it must be network related.
It was not network related. Well it could have been, but the sound bar needs a network connection really as does the TV.
I reset my router, gave the soundbar and TV it’s own ip range and wifi network and it still turned on.
So nothing other than the TV and Stage on a separate wifi network from everything else.
I reset the soundbar yet again and reset the TV after the lates update, this time leaving chromecast disabled on the soundbar set up and not installing any apps on the TV at all.
I have since added Youtube and Netflix and we have had a over a week without it turning on.
This is back on the regular mesh network as well.
So must either be Chromecast or maybe sportify, deezer etc. on the Stage or an app on the TV that was waking up the Stage.
One thing I did notice, was the lights on the stage lit up brightly before the TV turned on, which makes me think it was the Stage waking up the TV, but who knows?
Nice to have a few nights uninterrupted sleep! haha