Samsung, most likely, since it is unique to their device. I’d make sure you’re running the latest software for both the TV and the Sonos, and then contact Samsung’s customer service, as I don’t expect they have anyone assigned to reading Sonos forums. 

Thanks @Airgetlam. I have been reading that other TV brands like Sony has also been impacted so it seems more like a Sonos thing.

Have you tried the Sonos Arc connected to the TV’s optical connection instead? - it maybe the case that HDMI-CEC (AnyNet+) is the issue with your Samsung TV, allowing other devices to steal focus of the HDMI-Arc port.. it’s perhaps worth seeing if an optical connection resolves the audio dropouts.

I’ve got two Vizios of different vintages, neither exhibit this behavior. If this was truly a software issue with Sonos, I’d have expected one or both of them to have this problem.