Use wired connections or you will lose.

I've been using their equipment since 2005 and they have never reliably interconnected over the wireless.

Just spare yourself the trouble and wire them physically - they will be flawless.

What router do you like for wired SONOS connections? I have had ill luck with mixed generation Airports Extreme (1st and 5th).

I have a dedicated ethernet switch (rackmount cisco) that all of my ethernet devices plug into.

My router is a hop up the chain and does not interact with the sonos system at all ...

I was using ethernet over my power sockets previously, and that was no better.

Make sure that your Sonos devices and the devices you use to control them always get the same IP via static leases.

Using DHCP currently. I'll have a look at that when I get a chance.

Just configure your DHCP server to always hand them the same adress (static lease). Do you use the built in dhcp of your wifi router? Most of them offer an option to enter a mac address for which you want to assign always the same IP.

Sonos really does not like if components get different IPs after you had them powerless for some time while other components stayed active. I had the same issues you describe until I configured static leases for my sonos components and the smartphones we use to control them.

Thanks for the advice. Yes, I am using the DHCP of my router. I'll have a go at this. Thanks for the advice.

Sounds like something specific to your enviro. Haven't experienced that