It appears to be something to do with IP addresses, maybe.  I pulled out the network cable and plugged in one of the One SL and it came online. I disabled and enabled the Wi-Fi.  Unplugged it and it came back on. But as soon as I plug the second One SL in, my Arc bar and sub disconnects.  

Only wire one of the One SLs and do not Disable Wi-Fi in the wired speaker’s settings.

See if all your devices then show in the app.

The setting “Disable WiFi” does not actually disable WiFi, it turns off the whole radio. The radio used to connect to other Sonos as well as your Sub and Surrounds.

Power down all the Sonos and reboot your router.

Not sure if you have a Ethernet connected Sonos or not but if you do power it up first, then the other primary Sonos followed by the Sub and Surrounds.

If that fixes the issue use your router’s DHCP page to assign all Sonos a static/reserved IP address.

I’ve rebooted my router more times than I will bother with again.  One of the One SLs will stay connected indefinitely, as soon as I add the second they don’t make it through the night.  I’m about done dealing with it and will likely return them.  

When the speakers disconnect - do they actually lose their network connection, or can they still be ’pinged’ over the LAN/Showcas connected to the router with a DHCP assigned IP address? - also what router make/model are you using?

This reminds me of an old issue where the router is either running ‘Airtime Fairness’/‘QoS’ or has an issue with SSDP multicast/broadcast ‘discovery’ (IGMP snooping) and the controller device cannot discover some devices that ‘maybe’ on different wireless segments of the local network, or wireless access point, compared to the controller device 

It may also be helpful to know if you are using any security software on the controller device such as vpn software, antivirus, firewall, MAC spoofing etc.

The router is a Cox Communication Panasonic CGM4331COX 

The router app is pretty basic and I haven’t looked into pinging the speakers.  I would assume they aren’t losing network connection, I’ve been able to keep problematic Ring battery powered doorbells connected without issues.  
 

It’s just the basics out of the box network, nothing advanced, VPN, Firewall, etc.  A big reason for the frustration.  Everything else, Five, Arc, and Sub all work great.  The One SLs, not so much.  

I’m going to catalog my network devices to identify the One SLs.  I’ll then reconnect them and see if they are losing connection to the router.  Or if they are able to respond to a ping after they appear to disconnect from the system. 

@CraftBeerCFO,
Note the case the ring doorbells work is not relevant as they do not use SSDP multicast/broadcast for their device discovery - I would first try switching your setup to wired SonosNet mode by wiring one Sonos device direct to your router and see if that resolves your issue - see these support documents to perhaps get you started:

https://support.sonos.com/en-us/article/choose-between-a-wireless-and-wired-sonos-setup

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

In wired setup mode set the routers 2.4Ghz WiFi channel to either 1, 6 or 11 and set the wired device at least one metre away from the router

In the Sonos App goto ‘Settings/System/Networks’ and set the SonosNet channel so it is at least 5 channels away from your chosen router channel mentioned earlier.

If you have no Sonos portable products such as Roam or Move, then you can also remove your local network SSID/credentials from the Sonos App network settings (manage networks area) when all are showing WM:0 as mentioned in the earlier support link. That will stop your devices switching between the SonosNet signal and your router WiFi signal. See if that then resolves the One SL dropout issues as it will turn your Sonos setup into a wireless mesh setup, rather than having to use a connection to your router WiFi.

Hope that sorts the matter for you.

I’ve considered that but the tech I spoke to last said it needed to be the Arc that is set up for the SonosNet.  I can’t do that in the configuration right now.  I’m not sure I could would any of the speakers.  I’d have to relocate the cable line or run network cables behind the wall to pull that off.  Certainly not why I purchased them.  I’ll give it some thought.  I greatly appreciate your help!  

My understanding is that the One SL’s are not bonded as HT surrounds to your Arc in this case, so you can simply wire either of those standalone ‘Office’ or ‘Kitchen’ speakers direct to the router instead. If they are bonded as surrounds, then they both should be located in the same physical room as your Arc as they would be communicating directly with your Arc over an ad-hoc 5Ghz connection - you need to perhaps state which type of setup you’re using in this instance - if you see three+ Sonos ‘rooms’ in the Sonos App, Kitchen, Office etc. then you’re absolutely fine to wire either one of the One SL’s to your router (or the Sonos Five) to initiate SonosNet.

The One SL’s are NOT part of the Arc as a surround system.  They are in fact stand alone speakers.  I’ll look into this.  Thank you again!  I truly appreciate it!  

@CraftBeerCFO,

Even if you just wire one ‘Sonos One SL’ to the router, just temporarily as a test - set it one metre away from the router and just check all your speakers switch to WM:0 in the ‘About My Sonos System’ area of the Sonos App.If they don’t switchover then reboot them.

Then see if all do then work fine - you can go onto make all the other suggested changes mentioned/recommended later, but the simple switchover to a Sonosnet signal here I think shoukd work for you - just give things 15 minutes, or so, to settle down.

The Sonos interface stinks.  Just read this thread.  One would have to know a lot about network protocols to follow it.  I’ll never buy another Sonos product again.  My speakers don’t stay connected to my Wi-Fi and it takes ½ hr of trouble shooting every time I want to use them.