Are any of your speakers connected to the router by Ethernet cable at all…?

No. There isn’t any more space in the router, I’m using all ports. 

I’m not suggesting you do, I’m asking if you are because if so your speakers could be using Sonosnet and that could be at the heart of the issues. But you’re not, so my theory doesn’t apply…

Oh alright. Support never recommended that either. It’s frustrating to have a system that has been working for so many years, but I can’t seem to get two speakers to stay connected. I’m really trying my best not to rip them off the wall and throw them out the window. I might just sell them. I’ve been without surround sound for 8 years and only decided to get those two speakers in December last year. It’s not worth the effort at this point. 

What is the router and where is it physically in relation to the Sonos components? The Playbar uses the 2.4GHz WiFi, and then uses its own dedicated ‘network’ on the 5GHz frequency to communicate with the One SL’s as surrounds. 

If you setup the One SL’s as a stereo pair on your WiFi, do they work more reliably? I know that’s not what you want but might help narrow down where the issues are, and at least shows they are functioning. 

It’s an Archer AX12 and its located in the same room as my components and it’s right below one of the speakers. 

I’ve never tried that. Their purpose was surround for the playbar and that’s what they were set up to do. I’ll try remove them from the playbar later today and see if they work as a stereo pair. If that’s the case and they stay connected. Could it then be my Playbar that’s too old? Please don’t tell me that’s the case.

Is the router right below the Playbar by any chance? If so, that’s probably the worst place to have it so close to the Playbar, it might be stopping the 5Ghz signal from getting to the SL’s and Sub. In normal operation with the TV, the Playbar just gets its signal from the TV via HDMI/optical etc. so poor WiFi performance probably isn’t that noticeable. You can check in the Sonos App for the Playbar WiFi strength. 

If you need it there for ethernet ports, it might be an idea to get a small TP-Link switch for the TV area, and run a cable to it from the router so you can move the router further away. 

Also in the router under advanced, Network, IPTV/VLAN make sure that IGMP Proxy and Snooping are enabled probably with v2. Also look for uPnP and make sure that is enabled. Make sure you’ve updated to the latest firmware too. I’d also make sure OFDMA, WMM and TWT are disabled… they might not play well with Sonos. Finally look at the router 5GHz channel and move it away from where Sonos might be, so use a higher chancel number. I think smart connect needs to be off for it to work… 

https://static.tp-link.com/upload/manual/2023/202309/20230905/1910013387_Archer%20AX12&AX17&AX18%201.0_UG_V1.1.pdf

Is a link to the router guide …

My router is not below the Playbar, its places below one of the surround speakers cause that’s where it needs to be. 
 

All the network settings were messed with by Sonos support for two days. They got access to my laptop and my network settings and they were making it as it should. So I hope they did it correct. 
 

Sonos is running on channel 11.. I think 5GHz is either running on 1 or 6. 

Wonder if its a compatibility issue with the S2 controller app. Or an issue with mixing old hardware with new. I was having similar issue that was only corrected with downgrading my older equipment to the S1 app. My sub and one SL are newer and will not downgrade. So they are currently not part of my Sonos system.

An update:

I have without luck tried to connect my One SL speakers since I made this post and it is still not resolved. I have given up and decided to sell my Sonos system and buy a new brand. This breaks my heart because I’ve been happy with Sonos for a long time but they don’t seem like they wanna solve this issue. Customer service is not great and I have two speakers that are currently not in use because they can’t connect to my system. 
 

what a shame. 

Just as a last throw of the dice (and I’m not sure I’d assume just because Sonos have fiddled with your router, that the settings must be correct) have you tried temporarily moving the One SL’s close to the soundbar and away from the router to see if they then add? 

I have.. still nothing. They show up in my app as ‘not connected’, I restart the speakers and try again and they still don’t connect. I don’t wanna spend more time in this. The last 6-7 months has ruined it for me, I’m done with Sonos and as a start I’m getting rid of the One SL’s for a VERY cheap price because I don’t wanna make any money on this crappy system. I’m keeping my Playbar for now cause that runs smoothly as the only thing. But in time, it will go as well, to make room for something better. 

I can understand the frustration… good luck!