I'm using an Orbi RBR20 with 3 RBS20 satellites

Running into the same problem. I'm using an Orbi RBR20 with 3 RBS20 satellites, all running v2.7.4.24.

 

Things worked fine for years, and just started having problems within the last couple of months.

 

The issue appears to be between Amazon Echo devices that are connecting to different WiFi points. For example, when trying to set up a speaker group, if I add an Echo that connects to RBS20-A, any Echo connected to RBS20-B or C (or the RBR20 directly) will gray out with a "Network Error". Speaker groups that used to work can no longer be created.

 

I suspect it's some kind of network isolation between the mesh nodes' WiFi networks. Unfortunately, the RBR20 doesn't have any settings that would appear to control any kind of isolation. Perhaps there's something in one of the other Netgear devices.

 

It could also be some kind of change in the Amazon multi-room protocol that is depending on data of some kind that doesn't get repeated between mesh nodes. There's a 2021 Amazon Forum post that mentions the multi-room music feature uses TCP ports 55442 and 55443, and UDP port 55444. It doesn't suggest they're using anything like multicast or anything below IP layer.