Hi John ,
Thank you for trying to solve this. The answers to your questions:
1 the NUC is connected to a Netgear GS105. The devialet also (but the managed version GS105E). The router connected to the internet is a Ubiquity edgerouter X
2 both Devialet and NUC do not have WiFi configured
3 I only use one zone
4 the latest firmware version Firmware 13.0.0 + DOS 2.2.2 but the problem was also there with the previous beta 14 version.
Hope this helps.
Side note (probably not relevant) a managed netgear GS108E is connected to the edgerouter. NUC and Devialet are in the same VLAN. Never had any issues before or other network issues with any other device