The volume on the Arc Ultra should be adjusted via the TV, via CEC. The TV should relay the command to the soundbar. Question would be if this also happens when you use the remote that came with the TV.

That’s something to try if I can find the remote, lol.  Never used the original and don’t recall what it looks like.  When I got TV 3 years ago I programmed my Elite remote and never looked back. 

 If the Vizio Arc is the problem the other option would be to use my universal remote.  Problem is the remote won’t detect the Ultra but does detect the Amps on my network as mentioned before.  Thinking about it now I could wire this up after New Years to my Pool TV and see if it does the same thing.  
 

It may be that  Logitech or Sonos has not updated their devices which is the main reason remote does not see it. I would like a response to see if they are in the works for a fix or is it Logitech the one I should contact.

Logitech Elites, if I remember correctly, were IR only. Logitech stopped supporting all remotes’ programming years ago, it doesn’t surprise me you’re having issues. I retired both of my Elites, but mostly as I stopped using a multitude of random devices, and now stick with just the Apple TV remote, which controls my Apple TV and the volume on my TV, and via CEC (HDMI-ARC) the volume of the Sonos Arcs.

On the other hand, I abandoned Vizio, as the versions I had would send Dolby Digital Plus via ARC when using the TV’s internal apps, when taking a signal from an outside connection via HDMI, the most it could pass through was Dolby Digital. With their subsequent purchase by Walmart, after flirting with Chinese ownership, I decided to move to LG and Samsung, which used newer, and better chipsets for audio.

You could try contacting Logitech, but I’d bet you’d get a standard ‘we don’t support it anymore’ response. 

Thanks for the tip with using the Apple Remote.  I have verified the issue is with the Vizio TV.  With my Sylvox outdoor TV I am able to power off/on and each time the volume works on the Ultra.

Sadly, the Logitech Elites were designed before CEC became a thing. A great idea, I was unhappy when Logitech abandoned the space.

Maybe they ran out of names ;)

ISSUE SOLVED!

I have found a solution to the volume problem with the Vizio TV and Harmony Elite remote.  In the Harmony app I programmed 2 new buttons called “Sonos Vol Up” and “ Sonos Vol Down” using the Direct TV remote.  I programmed the Direct TV remote using the Sonos learn remote option.  Navigate to “Customize Device Commands Options”  Select your TV and select “Volume Up”.  You will be asked for a name, in my case I used “Sonos Vol Up”.  It will instruct you to point the remote close to the hub. When complete you will now see this newly created button in the Harmony App with your TV.  Do the same for Vol Down.  
 

These buttons will appear on the app but not on the remote.  We will now need to add these new command and assign it to 2 available buttons on the physical remote.  Go to  “Device Control Buttons”, select your TV.  Vizio TV and add these 2 new buttons by following prompts.  Once complete the buttons will control your Sonos Arc Ultra.  If you have any activities you will want to go to ‘Activity Control Buttons” and remap the buttons you select for your device in the previous step. 

The Elite has a “+” and “-“ located on the lower center of the remote.  These are used for home automation.  I do not use these and made sense to for me to use those buttons since they resemble the volume buttons.