Given the issues associated with Asus and Sonos, I’m somewhat hesitant to ask, but does Asus allow you to separate the WiFi channels for your main and guest networks? Based on your post, it seems like your guest network is causing enough wifi interference to be an issue for Sonos (and perhaps other devices). 

If I were you, I would recreate this issue, then submit a system diagnostic , and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

I use ASUS Wi-Fi 7 RT BE96U routers by 3 to create my AiMesh *

As the guest network will use 2.4Ghz/5Gz make sure it has a different SSID and password vs your main network. Most will assign a different password but not a different SSID. 

 * AiMesh is ASUS speak for mesh networks.

EDIT:

Also, if using the 6Ghz band for your backhaul be sure to isolate it to prevent the Guess network from using it.

I’m not going to say that disabling QoS didn’t resolve the OP’s issue four (4) years ago. However, there is more to setting QoS levels than just turning the feature on/off.  *

The OP stated that they had Video and Audio Streaming set as priority. That IMO is the correct setting versus the other options. However, the OP failed to mention at what level the others were set (which shouldn’t have been too critical) but setting the “type” of QoS to be used is critical. 

QoS has three (3) types of control: **

• Adaptive
• Traditional 
• Bandwidth Limiter

Adaptive is what I use and is probably the best in most scenarios. For the casual*** user the other levels require a bit more understanding of how they work and proper adjustment settings. 

Here are screen shots of my QoS settings:

As you can see I have chosen Adaptive QoS

The above prioritizations have served me very well for over ten (10) years using various models of ASUS routers configured in AiMesh.  Anyone who has read my posts on networking (and others wherein Sonos stability is a concern) knows that I have stated I have a very stable network (even through the App debacle).

So my point here is that even though the OP resolved their issue by disabling QoS they failed to mention (and/or show) parameter settings which may have been incorrectly configured for their use case.

 * My network consists of three (3) Wi-Fi 7 ASUS RT BE96U routers in AiMesh configuration with wired backhaul 

** Here is a link with more information on QoS parameters 

 *** I do not pretend to be an expert on networking by any stretch of the imagination 

Hi All,

Thanks for your replies, very useful.

The Guest Network uses separate SSID and password. However I think the guest network does use the same channel as the Main network.

QoS is off

I’ll have a go at submitting a System Diagnostics.

Also, the Kitchen system can connect to the AirMesh node via ethernet. Then the GuestNetwork no longer causes the Living Room Sub-Mini or OneSL to disconnect. Which is something I've seen suggested before.

So it's a work around for the full WiFi connectivity issue. But I don't think it's a WiFi interference issue.

Glad you found a workaround. However, I’m still not convinced what you are having to do is normal. I’d ask that in the RT-AX86U admin section go to Wireless settings, and then the Professional tab. Once there make sure AirTime Fairness is disabled for all bands.  

As mentioned I’m using three (3) Wi-Fi 7 ASUS RT BE96U routers that host 50 to 60 clients at anytime. Thirty-one (31) of those clients are Sonos of which none are wired to the main nor satellite nodes.

I can confirm AirTime was disabled for both bands.