I am having the same exact problems. With the HDMI connections. Gave up yesterday and connected to OPT but no matter what I did could not set it up to auto power up. I held down the power until you could here the tones increase but it still would not activat the auto power up. I have also noticed after updating from Ver 15.x to 16.x when powering it up the sub light no longer flash to let you know it’s connecting. And if you unplug the sub the light does not turn Amber however you can still tell the sub is on and the light on the back of the sub still works Amber when sound bar is off and white when sound bar is on.
I would have done retuned both the soundbar and the Sub if I would have purchased them local instead of online.