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.

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. 

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. 

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?

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