Couple of thoughts. 

First, try a simple network refresh, by unplugging all Sonos devices from power. When they’re all powered down, reboot your router. Once the router comes back up, plug back in the Sonos devices,

Second, in general, Sonos isn’t always happy with mesh networks, as the Sonos devices talk  to each other so that they can stay in sync. Many mesh networks tend to block that inter-speaker communication for a variety of reasons, which makes the Sonos system a bit challenging. I usually recommend a wired Sonos system in order to obviate those potential issues. The key to a wired system is the one device that you wire should be wired directly to the ‘root’ or ‘hub’ of your network, and not one of the satellites. You may want to try plugging a Sonos speaker or BOOST directly to your hub Velop device, and see if that clears up your issues. You’d need, of course, to be careful that the Sonos network is on a different and non-conflicting channel as your Velop of course. 
 

There’s some good information in the wired and wireless modes FAQ. 

Thanks for your help, much appreciated. I haven't been able to hardwire just yet, as I need a longer cable, but the full refresh has sorted the problem for the moment.

I noticed on my device list, on the Velop control panel, an extra Play 1 device, that when I clicked on it, said it was an Apple device, running iOS. I purged the device list, and it's gone for now. Can you confirm that shadow device should not be there (so if I ever see them again, I should remove them) or do the controllers come up as a device listing and it's nothing to worry about? 

Not offhand, no, since I’m not a Velop user. But I’d think that if you had a phantom device, and removing it from your network caused no issues, you’re fine. 

Hi Bruce,

My play 5 (1st ed) is now wired, but when I look at my devices, the play 5 is the only one with WM0. The others are all WM1. If they dropped out to reconnect to the wired device, they did it very quickly.  Have I successfully changed it to wired, if only one device is shown as wired? Thanks

You probably should remove your WiFi information from the controller at this point, as discussed in the remove Wifi data FAQ. Sometimes a power cycle is needed to nudge the device from one connection to the other. 

I cannot select the network in the app to delete it. It just won't let me. The network name is listed under In Use. I tried turning off all devices, other than the wired device, but then the network name disappears from system>network. When I turn the devices back on, they reappear as WM1, the network name reappears, and still it can't be selected. I tried with iOS and Android apps, and turning devices back on in different orders. Any ideas? Thank you

I got there. I left the one wired device on, changed the password on the router, started one other device back up, was able to delete the network, now they have all bumped over.