I have been having the same issue for months. At first I thought it was the unique combination of my Samsung OLED TV, Sonos Arc and Apple TV. Lots of forum chatter about this at Sonos and Samsung. It went away for a while when I changed HDMI cables, but now it’s back (I suspect with a recent software update). For me it was more than just Netflix: same issue when streaming Atmos content from Apple TV+. So I thinks it’s an Atmos issue rather than just Netflix. The fix for me was to use the Netflix and Apple TV+ apps built into the Samsung TV. No issue with those, so seems to be a problem with the Apple TV 4K. Really disappointing that Apple hasn’t fixed this.
I wished this had more visibility. I would like to add, in addition to Netflix, it happens on all Atmos content, even from AppleTV+, albeit not as frequently. For me, the problem is also accompanied by "popping/clicking" and will sometimes result in my AVR losing the decoding, waiting to "sync" back up. Likely related to MAT 2.0 timing. Since Netflix incorporated the tvOS 15 native player with a recent update, the problem seems less prevalent, but still exists. Frustrating is an understatement.