A stable ethernet connection should not allow a device to switch between WIFI and ethernet.

Are you hardwiring the Ultra to a mesh node? Sometimes this can cause issues. 

Are you using a good ethernet cable?

It is recommended that you hardwire to the main node/router or a switch connected to the router.

Here is what to look for in “About My System”:

https://support.sonos.com/en-us/article/check-if-sonos-is-in-a-wireless-or-wired-setup

I have the Ultra hardwired to an Asus XD4R (AX1800 Dual Band WiFi Router), which is the main node of my mesh system. The XD4R is connected to the network via a switch, and I’m using a good-quality Cat5e Ethernet cable for the connection.

Despite being hardwired, the Ultra consistently switches back to WiFi. I’ve attempted to disable WiFi for the Ultra in the Sonos settings, but it automatically turns WiFi back on, and the connection remains unstable.

Could the switch or main node configuration be causing this behavior? Should I bypass the switch entirely and connect the Ultra directly to the router, or are there additional steps I can take to force it to remain on Ethernet? Any advice would be greatly appreciated!

There was a system update that came out this week. Have you updated? Give it a shot if you have not done so. It may cure your issue.

Is there a reason why you want to hardwire the Ultra? Do you have connection issues when on WIFI?

If not, you may want to explore that option to see if it works for you.

Are there any other speakers hardwired on your network?

Thank you for your response!

Yes, my system is fully updated as of this week, but the Arc Ultra still switches back to WiFi. The reason I want to hardwire it is to ensure the best possible connection and address voice sync lag issues. I believe these issues might improve significantly once I integrate an eARC switch into my setup, as my current TV lacks proper eARC support.

I don’t have any additional speakers in the system yet, just the Arc Ultra. Is there anything specific I should adjust to force it to stay on Ethernet in the meantime? Or should I wait until the eARC switch is installed to fully resolve this?

I suspect that there is something wrong with the Ethernet connection.

Every time I’ve seen a Sonos swapping back to WiFi from a wired connection it was a cable problem. 

Personally I’d spend my time getting the WiFi working properly. If you plan on adding a Sub or Surrounds disabling the radio they normally connect to is likely to prove quite frustrating when you try to get them to connect.

I recently un-wired the several Sonos I had wired and moved to WiFi only. Rock solid and I no longer have to give up one of the three clear WiFi channels for the Sonosnet connection.