Error with Plex: "Unable to play [track] - the connection to Plex was lost"

Do you have UPnP auto-port forwarding enabled on the router? If not, then try enabling that aswell as forwarding port 32400 to your Plex server and see if that resolves your issue. I’ve read (somewhere) that some routers need to have UPnP enabled for things to work. That said my Plex server/Sonos service work fine without it, but it still maybe worth a shot.

Thank you for the suggestion. Originally, I had manually forwarded the needed port for Plex. I changed this to use UPnP instead, but it made no difference. Playback on Sonos continues to fail with the same TLS error being displayed by Plex:

CERT: incomplete TLS handshake from [::ffff:xxx.xxx.x.xx]:35841: no shared cipher (SSL routines)

It appears to be some kind of certificate error, but I would have no idea how to resolve it, or whether the problem is on the Sonos or Plex end.

Since the service is apparently working for others, it could also be something with my LAN or router, but from what I can tell, my environment meets all the necessary requirements.

Did you try manually forwarding the port aswell as enabling UPnP, rather than instead of? 

I also came across this link when searching for the error … maybe something in the thread will assist you:

https://github.com/RasPlex/RasPlex/issues/645

I'm not sure this is possible for Plex.

In the Plex Media Server admin UI, these two things seem to be mutually exclusive. After disabling custom port forwarding on my router for Plex, I had to disable the manual port forward setting in the Plex Media Server in order for it to create a connection via UPnP. Reactivating the manual port setting seems to clear any existing UPnP connections.

UPnP has always been enabled on my network, even when I was using manual port forwarding, for what it's worth.

Thank you.

From reading through this, it seems the most salient suggestion was to disable authentication for local clients. I do not believe this can be applied to Sonos, since Sonos always streams from a Plex server remotely, and not from a direct LAN connection, if I understand its design correctly. 

I’m also running the same Plex server version 1.32.5.7349, albeit on my Netgear NAS box, but presently use it with the S2 App… give me a moment and I will check the server with the latest S1 Sonos App and report back.

I added the Plex service to the S1 App v11.10.1 and Plex-audio playback is all working okay here (see attached) - so I guess it’s likely going to be something local to your setup, perhaps?

Have you ever had Plex working with your current router/network setup, or is this a new setup? If it’s new, maybe it’s a setting on your Eero router that’s blocking access🤔? Any firewall etc?

@Ken_Griffiths: thank you so much for doing this testing. It is encouraging to hear that it all works as designed in your setup. 

I agree it is likely something local to my configuration, but I have investigated all the usual suspects. Eero sadly does not expose many advanced settings to tweak, though I can have another look.

The only interesting thing about my current setup is that I transferred Plex to new hardware recently, using the standard process described here: Move an Install to Another System | Plex Support. But I have done this multiple times, and nothing untoward happened with this migration.

One thing I have not tried yet is to log out of my Plex server altogether, and then “reclaim” it. I will give this a shot and see if it helps, and then report back when I am able.

Well, I got this sorted.

The problem was that the Plex advanced network setting for secure connections was set to “required” instead of “preferred”. After making this change, I can now stream from Plex again.

This was unexpected, because Plex explicitly lists Sonos as supporting secure connections here:

How to Use Secure Server Connections | Plex Support

This leads me to believe that there may still be an issue on the Sonos side that would be worth looking into, since the behavior does not match what Plex describes. I don’t know if the Sonos developers monitor these discussions, but I’d be willing to offer more information to them if needed.

For security’s sake, I would prefer to run my Plex server requiring secure connections for all apps, so I hope that this could be addressed by Sonos in the future.

@Ken_Griffiths : thank you for your efforts to help with this. 

Thank you @Corry P.

I have opened a similar discussion and reported my findings on the Plex Forums, and hopefully their devs will see it. I will consider opening a support ticket too.

I believe that “Preferred” is still the default setting for secured connection in Plex, even when remote access is enabled, so I’m not super concerned about the security risks. I imagine this is how most Plex servers are set up. But it would be nice to get this to work. I remember I changed this to require secure connections some time back, but I guess I never tried streaming from Plex on Sonos until recently.

I appreciate the consideration.

Yes, FWIW, both my Plex servers network connection are set to the (default) ‘preferred’ setting and I’ve tried the setting as ‘required’ and found it doesn’t play the tracks in the Sonos App, but I can still view the entire library/tracks. The App even appears to load selected track(s) to the queue, but then fails in their playback … I quickly used an https secure connection to the Plex server to change it back to ‘preferred’. It will just stay at that default for now. Glad you got things sorted @User246959. 👍

I have same issue… my Sonos speakers are on one router and plex server is on another one.. I dont see issues watching movies, but issue is with only songs.  When I check logs, connection is coming from outside network.  

When I use plex amp the connections are similar and works ok, but when triggered with Sonos app it fails. Remote access is enabled in configuration, and it shows working.

I cannot move server onto same network IP. 

Able to fix it.

For some reason Sonos app only works when I disable remote access by removing port forwarding in router.

Now app uses WAN for connection and everything works as it is supposed to. 

One more  issue, Sonos app stops working when upgraded to 1.32.7.7571.  

It is working properly when on 1.32.5.7328

I did not test versions in between. 

Who needs to fix this Sonos or Plex ???

Looks like Plex upgrade caused the issue.  I have to revert to 1.32.5.7328. 

1.32.7.7571 did not work.