As you’re using a WiFi mesh setup, perhaps take note of the suggestions mentioned in this thread:

https://en.community.sonos.com/troubleshooting-228999/troubleshooting-sonos-on-wifi-6856334?postid=16520976#post16520976

HI Ken! Thanks for the response. 

re: the mesh setup, I’ve disabled the radio on my upstream router, so I don’t believe that should be an issue. Furthermore, the “cutting out” issue doesn’t present itself with music, it happens only with TV. Very strange!

The surrounds communicate with your playbar over their 5Ghz WiFi adapters in an direct ad-hoc connection so it may often help power-cycle the playbar aswell as the surrounds and perhaps keep any other wireless products well out of their way and/or put them on the 2.4Ghz band. If you are using SonosNet as suggested in that article, then I also recommend the following:

• Ensure and wired device is at least one metre from the router (do not wire HT surrounds or it’s Sub). Ensure the SonosNet channel is set at least 5 channels away from the routers chosen channel and still set the channel-width to 20Mhz on the 2.4Ghz band to simply reduce WiFi interference overall.
• If not using and Sonos portable products then remove the local WiFi credentials stored in the Sonos App network settings
• Do not switch off the WiFi adapter on any of your devices.

See if doing those few things resolves the audio dropouts on your HT surrounds.

One further thing to try is a different optical cable between TV and playbar, but perhaps leave that one  just as a very last resort.

Unfortunately I have more questions.

1. I didn’t see in that article where it suggests using SonosNet. Could you point me to that? I do not currently have any Sonos device wired directly to my main router gateway (eero), nor to the upstream router which has radio turned off.
2. I don’t know if I’m using SonosNet. It sounds like I’m not, because I have not wired a device to my router. Is that correct?
3. If I do use SonosNet, how can I ensure the channel is set at least 5 channels away from the router’s chosen channel? I’m guessing (a) I need to figure out the router’s channel rthis is easy] and (b) figure out how to set the SonosNet channel othis is what I do not know how to do].

My next step for now: I will try power-cycling the playbar and surrounds to see if that works.

Thanks Ken!

Whilst Sonos will work absolutely fine with many mesh WiFi systems, in fact a mesh setup is certainly preferred over wireless extenders/repeaters - a system clearly also works great on its own internal and entirely separate SonosNet signal with one device only wired to the primary mesh hub/router - so it’s worth trying SonosNet as it can often handle SSDP multicast discovery and grouped-room playback better than some mesh wifi setups with different hubs operating on different WiFi bands & channels. The fact the SonosNet network is ‘exclusive’ also has obvious benefits.

So that’s why I and many others here suggest using SonosNet alongside a WiFi mesh network… in some cases it’s possible to fix channels on WiFi mesh hubs.. in the Eero case I’m not sure if that is an available option, but i was merely highlighting to try to use a non-overlapping WiFi channel for SonosNet, ideally not one used by Eero.

I had the same problem and my solution was toe enable wifi on my arc (which I disabled since it’s connected with lan). The rears connect directly to the arc with 5GHz which make sure a they are in sync. 
 

on my Google wifi the rears are now reported as connected with wire (bridging via arc)

Sonos has confused so many people with that “Disable WiFi” option.

Yes it does actually disable the WiFi but it does it by turning the radio off.

That would be the radio needed to connect with a Sub or Surrounds.

Some day it make it onto the developer’s to-do list but today is not likely the day.

Turning on WiFi in arc solved my surround music tearing issues. This should be fixed in the software:/