Seems odd. I’d certainly check the Hisense TV for updates. As near as can be garnered from your post, it seems to be blocking the surround channels in some way, although I’m not sure about that. It could be worth adjusting the volume for the surround channels in the controller, too.
Ultimately, though, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.
There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.
When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.
Just as a random thought, the pair of Ones are actually set up as surrounds, and not just a separate room that is grouped?
Just as a random thought, the pair of Ones are actually set up as surrounds, and not just a separate room that is grouped?
They are indeed set up as surrounds. No hope with increasing volume of the surround channels either. Just quiet static noise.
I'll try going through the system diagnostic route. Thank you so much!
Like I said, it was a random thought 
There are some who don’t realize the difference. Obviously, you do!
But I have no real answer, other than my derision of Hisense being a Chinese company, and not always implementing various standards (in my view) properly. On the other hand, you have it set to pass-through, so it ultimately shouldn’t make a difference. However, being a US based person, I’m not familiar with the SkyNet / Sky Stream settings, I expect Sonos CS to help figure it out.
