That’s odd, it should only stream/ AirPlay 2 to one of the stereo pair, and the other should play the signal as well. It does on my S2 system. And in fact, if the devices are just grouped, rather than a stereo pair, it still functions.
I think it might be worth a reboot of your speakers just as a precaution, to see if for some reason a reload of the OS helps. But if it doesn’t, I would recommend that you submit a system diagnostic within 10 minutes of recreating 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.
I’ve just quickly tested the issue here and Airplay2, using Apple Music App, is playing to both my One’s (stereo paired) …and it works with Fives (paired) too. So I think the same as Bruce above, that it’s something local.
In addition to rebooting the speakers, I would check the router settings and ensure the 2.4Ghz WiFi band is using a fixed non-overlapping channel (either 1, 6 or 11) and perhaps set the channel-width to 20MHz only to reduce the potential for wireless interference and see if that resolves the issue.
Online there are also these suggestions for sorting Airplay issues:
- Toggle ‘off’ Bluetooth on the sending device, or if already ‘off’, try turning it ‘on’.
- Turn off Cellular Data
- Disconnect from any other Bluetooth devices (like speakers)
- Connect all devices to the same WiFi network Access point
- Reset your network settings on your iDevice in Settings > General > Reset > Reset Network Settings
- Update iOS, and speaker firmware/software
- Move the devices away from other electronics
- Renew your devices DHCP lease via the router configuration pages or reboot the router
- Switch off any security software and VPN software installed on the broadcasting device.