I’d try a reboot of three things. First, your router, and give it several minutes before testing.
Second, I’d power cycle the Sonos speakers themselves. Again, give them a few minutes to fully reboot and log back in to your network before testing.
Finally, and the thing that has ‘fixed’ this issue for me in the past, a power cycle of your Apple device that is generating the AirPlay 2 signal. Seems like you’ve done that with your Apple TV, but I’d do that with your iPhone, too. The three times a similar event occurred to me, that’s what has fixed it.
My issue similar although Roam and other OneSL still connects/plays. I’ve done all the things listed here but the one normally rock solid OneSL “cannot connect”. Any ideas? Updates completed. Router cycled. Devce cycled. Sonos One SL cycled. multiple times.
Not offhand, sorry. At this point, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.
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 phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.