Hi @Eric F
Thanks for your post!
The most common fix for audio interruptions from a TV is to reboot the TV by unplugging it for at least a couple of minutes. The type of glitch solved by this typically affects all apps/sources, but it’s definitely worth trying if you haven’t already.
With HDMI-over-Ethernet being involved, I would be tempted to temporarily move the front Amp and connect it directly to the TV, bypassing the ethernet altogether. However, given that all other apps work without issue, it’s a long shot - I’d try it only if nothing else helped. However, such setups are unsupported by Sonos - it’s not that they won’t work, just that we can’t help if they do not.
I would also test with the TV’s own speakers because if the issue occurs there too, it’s clearly nothing to do with the other equipment - Sonos or the HDMI-over-Ethernet setup.
For me, this rules out the “app” portion of it being Samsung’s fault since Samsung’s YouTube app is Tizen based and the Chromecast is Android based. Could still have something to do with Samsung’s audio engine, ARC port, etc… I’m not sure exactly if the TV would be doing anything to the digital audio other than passing it directly to the Sonos AMP.
That entirely depends on the TV’s digital audio output format setting. “Passthrough” should do exactly that, leaving the audio untouched, but TV manufacturers seem to be playing fast and loose with the definition these days. You may actually be able to resolve the issue entirely by telling the TV to convert all audio formats (including PCM stereo) into Dolby Digital with this setting.
For what it’s worth, when using Passthough on my HiSense TV (also with an Amp) I get similar, tiny glitches, but not nearly as frequently. If I switch to Auto, they disappear (but I can no longer play DTS, which is why it’s on). This seems to affect all formats, though I haven’t really tested to be sure - certainly with Dolby Digital 5.1. I am contemplating turning Passthrough off for this reason - it’s a little annoying, but if it was happening to me as frequently as it is to you, I’d have turned Passthrough off soon after getting my new TV last month. I still might, as most of my DTS movies are DTS-HD and are converted to Dolby anyway.
I’m thinking this is likely a Sonos issue, perhaps something to do with the Opus codec being used by YouTube in conjunction with the two Amps being set up for virtual surround.
In your own words, “other apps work fine”, but two versions of YouTube play with issues and you blame us? That seems unfair - but we are used to it! 
Do you have another TV you can test with? If you can reproduce the issue on another TV with a normal cable connection, then you could be correct - but it won’t be because of the surround sound setup (which isn’t virtual). If it is the Amp (unlikely, but you already know I think that) then swapping the two Amps - as in, remove the surrounds in-app, wire the other Amp to HMDI and add first Amp as surrounds to it - would confirm an issue with the Amp currently with the HDMI connection.
When I download some music videos off of YouTube via yt-dlp and put it on my Plex server those videos play find on the TV but it that case it’s not using the Opus codec, it’s using AAC audio.
When you play YouTube, the app outputs PCM to the host device running the app just like any other media app (Plex) and the compression codec used in transporting the media, Opus or AAC, is irrelevant - to Sonos and the TV, at least. The YouTube/Plex app does the decompression. The TV just passes the result along, and the Amp will play the PCM it receives. If the Amp were receiving Opus, you would not hear anything at all as we do not support that codec.
I hope all this helps.
