1 Sonos speaker out of 6 keeps dropping out

I have a Sonos Arc, Sonos Sub 2, a pair of Sonos 300s and another Sonos OneSL that all work flawlessly. Never drop, never disconnect. Same network same room. 
Not the wifi, not the network. The problem speaker worked for 4 years without issue. Not only does it drops it disappears from the app entirely. 
 

Issue has been replicated both on WLAN and LAN. Also not in a stereo pair with the other Sonos One, same thing. 
5 out of 6 Sonos speakers work. It’s punishing to go over this week after week. 

If it happens when the device is wired too, then I’d perhaps speak/go-back to Sonos Support and provide them with any details/diagnostic reports you may have obtained thus far and see if they can maybe assist you further. 

Hours of Sonos support hasn’t resolved this. 
another confirmation that it’s the app. Sonos OneSL gave this error, switched over to Arc system to play same content without issue  This is fed by the Sonos app. 
 

The Sonos App does not ‘feed’ anything ​@BigAlNYC - it’s not a music player, it’s simply a ‘remote’ (software) controller App, that causes the audio source to play ‘direct’ on your chosen Sonos room/group… it’s more likely a network issue, or possibly a fault somewhere along the path from the source audio to (and including), your One SL speaker,  that’s based on what you’ve posted here.

What was the speakers SNR dB level when this error happened (assuming the speaker is not in wired mode)?

​@BigAlNYC - note that any audio source that you begin playing on your Sonos speaker(s) from within the Sonos App should carry on playing even if you fully close the Sonos App and/or power off the mobile device on which you have the App installed.

If the music source is stopping, or not playing on your One SL speaker, but happily plays on your other speaker(s), then look at the network segment & connection that particular speaker is using. Look at any connection signal level and it’s position, for potential interference (wired or wireless) interruption etc.

Clearly we (as other Sonos users) can’t rule out a hardware issue either with the speaker itself - only Sonos Staff will likely be able to do that with your diagnostic data, as mentioned earlier.

If the issue persists and you are easily able to reproduce the matter,  then gather any information/data and re-contact the support Staff. The diagnostic data should help pin-point the causes, hopefully.🤞 

Thank you for your responses.  And if I use non technical terms as “feed” please excuse me for reasons of brevity. 
The Sonos app is the music source. I also use Airplay for Twitch and Mixcloud content. My point was to highlight the audio source (Sonos app) and the Sonos OneSL error, while the Sonos Arc in the same room played immediately. After several weekends of troubleshooting I’ve resigned myself to this being permanent. 
 

The App is not a music source, it is only a remote for the Sonos speakers that fetch the music from a source.

Confirm this easily, pick something and play it, now turn off the controller's host device and note the music continues.

I disagree. If I want listen to Spatial audio on Apple Music only the Sonos app allows me too.  Airplay doesn’t support this high res format. Only playing Apple Music “through” the Sonos app allows for Atmos (Spatiall Audio). So the Sonos app is a conduit for lack of a better term to facilitate this high quality audio format.  

Sidebar: This back and forth on technical terminology and what is or is not the actual “source” is a time waster. 
The one speaker stopped working. All other Sonos speakers on the same network work. 

@BigAlNYC,

As @Stanley_4 mentions above, the Sonos App is not a music source…  The App is also not a music player, much in the same way that a hand held ‘TV remote’ control is not a video player. 

If a movie did not play/stream on your Living Room TV, but worked fine on your Bedroom TV, you would likely not blame the ‘TV remote’ for that playback problem. So you are likely looking in the wrong place if you are saying the Sonos App ‘remote’ controller is the cause of your issue… the answer to your problem ‘more likely’ lies elsewhere. 

I can only repeat what I said earlier… take a closer look at the network segment & connection for that non-playing speaker. Look at its connection signal level and its position in your Home for potential interference (wired, or wireless) interruption etc.

Sonos community users here can’t rule out a hardware issue with the speaker itself - only Sonos Staff will likely be able to do that with your diagnostic data, but my own thoughts are, that the answer most probably lies somewhere within your LAN subnet and local network hardware setup anyway. The simple fact another Sonos speaker plays/streams the same audio source ‘directly’, certainly does not  infer that the Sonos App is the likely culprit here.

Again thank you for your very quick responses  But let’s take a moment for 30,000 FT view,  large part of Sonos’ popularity and success was due to its simplicity. I’ve recommended Sonos brand to numerous users and friends who asked for my advice regarding whole home wireless audio system products. LAN subnets and network channels are way above what the average user can comprehend. Sonos has lost their way. Numerous YouTube videos on this topic.