Is UPnP a rubish protocol ???

[stefano_mbp]

... so renderer (Klimax) and Synology are connected to a switch (*) which is in turn connected to a Mesh antenna ... I don't know Mesh networks, I have a wifi network based on Apple Airport Extreme and Airport Express (which, however, is only used by the tablet ... and is very stable).
Could you try, at least temporarily, to connect the switch (*) to the router (thus eliminating the wifi network)?
… btw … when your Klimax disappears is it still on the network? That’s to say : can you find it using a network scanner like Fing? or using another control point app like Linn or MConnect?