After router change (Asus RT-AX88U → Synology RT6600AX) Roon not able to finde Airplay and Chromcast Devices. Multicast and IGMP Snopping ist activated. Devices not listed under “Settings\Audio”. Sonos, and Netork streamer (Roon Ready) works fine. Core is a Nucleus+.
What I’ve tried so far:
- Stop Server Software, rename folder “RAATServer”, Reboot Core.
- Backup, rename folder “RoonServer” an restore from Backup.
- Reboot, Reboot… everithing more than once
… nothing of these could help.
I can’t say exactly when this problem started. I saw it today when I wanted to integrate Chromecast as a display. Similar Problem with Ropieee. Have two devices but in the WebUI i can see only one under menu Devices
Something doesn’t seem to be working properly in my network
Sorry, english is pretty hard for me 
Problem solved:
Wenn reboot network switches, some Airplay devices are shown. After a few minutes they disappear again. Switches are managed, Multicast can be configured. Set from unconfigured to “any” will solve the problem immediately. Now i can see devices never seen before 
Everithing working fine now including Ropieee:
Best regards