I doubt that the audio drops have anything to do with your Arc. It’s more likely your network.
Streaming video especially 4K takes considerable bandwidth over WiFi. You may have 1GB inbound to your router over Ethernet cable; but it diminishes over WiFi. Using your AppleTV 4K over WiFi can be problematic unless you have an exceptional WiFi signal. If you are using access points, range extenders or a mesh network WiFi issues can be exacerbated with HD-Video/4K.
Here is how Audio/Video is sent to your TV then Arc
- WiFi or Ethernet Audio/Video Stream > AppleTV 4K > HDMI Out > TV
- Video > TV
- Audio > TV HDMI Out > Arc HDMI-In
WiFi can deliver an inferior signal causing drops in audio to Arc. If possible try connecting your AppleTV 4K via Ethernet to your (main) router. See if that changes things.
However, if you think it’s your Arc submit a diagnostic to Sonos within 10 minutes of the occurrence and post the reference ID in this thread. You can then call Sonos Tech Support to discuss. Click here.
Do you have any other devices connected to the TV? Does disabling eARC on the TV make any difference? Have you tried a different HDMI cable for the Apple TV?