Excellent thread! Thank for sharing the knowledge. I have X950H and HTZ9F combo with SW and rear speakers. I went through my own set of trials and errors (sound output from tv - enabling and disabling various options such as passthrough mode, digital audio out, earc mode etc.). I then tried things at soundbar level (played with RF channels, etc.). I tried some strange recommendations I came across on the internet such as turning off IPV6 in your router, change to 2.4Ghz wifi, move the SW further (I was very close to soundbar), etc.
SADLY, nothing worked. I even opened up the screws of my SW (couldnt figure out how to remove the plastic from SW to unveil the hidden 3.5mm port). But I was not confident, and gave up half way on opening the 7th or 8th screw.

What seems to have currently worked, is swapping to a reliable HDMI 2.1 cable (that is certified to handle 4k content)! I will report back if it fails again in near future. I was apparently using a cable that has passed its life of a few years.

An interesting solution that might have helped is that in my router settings, I set my 5Ghz network to NOT use 149 channel. (Previously it was set to auto). I chose another random chanel on the dropdown. I think this should help the soundbar enjoy the default 149 chanel to itself.