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.