Enable TV Autoplay under the Arc’s settings in the Sonos app.

I suspect this doesn't quite address the question. I don't think this is a failure to switch back to the TV as audio source. It sounds like TV is the audio source but is muted.

Could @paulan please confirm / refute?

Thanks for the suggestions. I spoke with a Best Buy technician and they said that the Arc goes into standby mode when the TV is turned off. That’s why I have to increase the volume when the TV is turned back on. 

It seems to behave differently on different TVs. When I turn mine on, the Arc starts at 0 volume, but will then gradually rise to whatever level it was at when the TV was last shut down. 

Hi

I don’t think it’s the Arc. I have Xfinity as well and I suspect it’s the way Xfinity handles the video and audio signals sent to the TV. IMO I believe the Xfinity box sends the video first and audio later. It’s not that noticeable via a direct connection to the TV but given the CEC handshake to the Arc it becomes more apparent. I say this because when I had Google Fiber no such delay existed.

I only switched to Comcast/Xfinity because Google Fiber discontinued their hardwired cable service in favor of all wireless streaming boxes. The Services offered are YouTube, Fubu and Sling all of which have a minimum $35 monthly fee. I was not impressed with the programing choices as you had to pick one from column A and one from column B and one from column C (so to speak) respectively to build the package you desired. That became very expensive in a heart beat. Neither was I impressed with the video and audio quality of any of those streamers.

So...all said IMO it’s Xfinity. Just something you may have to live with.