Not an expert here, but as soon as you say “Sonos BRIDGE”, the first thing that pops to mind is the potential for the power supply to go bad, as has happened with many other of those devices. The power supply, when it starts supplying a variable voltage to the BRIDGE makes all sorts of difficult to track down issues appear. 

I’d be tempted to do some testing by pulling the BRIDGE out of the equation, and at least temporarily wiring a Sonos speaker directly to your router. If that “fixes” the problem, then you should likely consider either leaving a speaker wired to your router, or replacing the BRIDGE with a BOOST, which is the newer, better version of that device. It runs S1 or S2, so if you’re still on S1 (which you must be, due to the BRIDGE), so there’s no worry there. You could conceivably also just set up your system to hang directly off your internet signal. See the wired and wireless modes FAQ for more information.

You could conceivably replace just the power supply to the BRIDGE, but at the cost of a replacement power supply, not available from Sonos, it’s not that much more to purchase a BOOST.

Yes, I agree with Bruce, this is likely the ‘old’ (much talked about) Bridge power supply ‘fluctuation’ issue. There are 3rd-party power supplies that may replace it, but simply wiring a Sonos device in place of the Bridge should sort it too …and at the very least that can be used to test the theory that the issue is Bridge-related.

The Bridge is most likely the problem. It’s software/firmware is outdated and known to cause problems. Remove the Bridge and wire a speaker (except a surround, Move or Roam) to establish the SonosNet or replace it with a Sonos Boost ($99-USD). 
 

Edit: @Airgetlam and @Ken_Griffiths got there remarks in first…So, what they said

Thanks for yur speedy replies gents.

@Airgetlam do you mean plugging a speaker into the router or the google hub. I thought with a google hub the bridge/boost should go into that?

@Ken_Griffiths I could relocate a speaker to test the theory - is it as simple as plugging or is there some re-pairing of some kind needed? It’s been so long since I set it up I’ve forgotten the steps.

Re conncting to the wi-fi, doesn’t that mess around with the google hub mesh? I know I had to set up a separate SSID for Sky Q as that liked to argue with google - and I was always the loser 

Ok, so I disconnected the 10 year old but up until now reliable bridge, lugged a Play 3 downstairs and connected to the Google hub, established a wireless network, disconnected and resited Play 3 and so far all is good via my wireless network.

Fingers crossed it stays connected! 

Thanks again all.

So, too late, but I meant that the wired Sonos device should be wired to the device that functions as the DHCP server, which is never a extension puck, and usually the base device of the system. In your case, the Google Hub is the router. 

Honestly, my opinion is that Sonos doesn’t play well with most mesh networks. Not a reflection on either Sonos, or the mesh networks, but Sonos expects to be on a single subnet, so that each speaker can ‘talk’ to the others, to get information. Many ‘mesh’ networks function by breaking the network into multiple subnets. Which is fine in most cases, if you’re not Sonos. So, I’d recommend your current state, a ‘wired’ network, with one Sonos device wired to the ‘hub’ of your Google mesh. It is up to your situation if you leave that as one of your Sonos speakers, or deploy a BOOST. I happen to use a BOOST since none of my speakers are in close proximity of my router, but both setups are essentially the same. 

I was far too hasty to post the wireless solution had worked, it fell over very quickly and only one device could even find the system on the network, before it lost it too. 
 

I’m going to connect a speaker to the Google base and see if that does the job, which it should do. Assuming it does I’ll buy a Boost for the same reason you have. 

If I understand your setup correctly, the Draytek is merely serving as a gateway to get the stream to the Google device, which is operating as the DHCP device. Since your controllers are connecting to that Google signal, and not the Draytek signal, that’s where the Sonos device should be wired, to the Google base device. 

Just as the BRIDGE was before. 

Since I got name-checked I’ll add my two penn’orth. All the symptoms suggest the Bridge power supply has indeed failed. I’m surprised it lasted 10 years. 

I’m just wondering aswell, if the VM Hub 4 is set in ‘modem mode’ and the Google Nest WiFi Primary Hub is the router, then why the need for the Dreytek device in the middle? - I’d just remove that, that’s if it’s built-in ‘switch’ is perhaps not needed?

Thank you all again, and to @ratty for chipping in. It would seem that the root cause of the problem is ME. The Draytek is used to provide a second SSID to which the Sky Q connects and being the idiot I am after the factory reset I stupidly set up another SSID which matches the Google Nest one. No wonder Sonos couldn’t work out whether it was supposed to connect to the wireless or the wired connection.

Since deleting the duplicated  SSID the system has connected ia a Play 3, but I’m going to reinstate the trusty old bridge.

@Ken_Griffiths, I think there’s a way to connect the Sky Q via the Google hub without the two having a row, and maybe I could get rid of the Draytek but as you can tell this isn’t my forte! 

Ah yes, the Draktek's SSID would have been on a different subnet, as the Google primary hub by default contains a router.

Frankly I’d still replace the Bridge. Notwithstanding the tendency of its power supply to fail, and that it can only run S1, but its wireless tech is the ancient SonosNet 1.0 with its lower range and resilience.

Thanks ratty, so essentially just replace it with the Boost? I must admit I’m very happy with the S1 setup and only really need to maintain what it’s already doing. Not Sonos related by re the question about why have the Draytek it has other “things” plugged in e.g. wired cctv and the google hub doesn’t have that level of functionality.

What’s most frustrating is I’ve just had VM installed with the 1Gb connection, but for some reason that’s still under investigaiton in modem mode connected to the Draytek I’m getting hopeless download/upload speeds.

Personally I would. I’ve lost count of the number of cases here where a failing Bridge power supply was found to be the cause of strange, intermittent, frustrating, connectivity problems. Your Bridge entitles you to 30% off a Boost.

I can’t comment on VM, but when measuring internet down/up speeds it’s important to ensure that they’re not being throttled by something else such as WiFi. Use a PC wired to a Draytek LAN port. If your PC is hardened for direct internet connection you could even start at square one and wire it directly to the VM box.

Thanks for the thoughts on the Boost, and with 30% off it sounds like a good idea!

The bizarre thing is if I conenct a laptop as you describe it returns at best 200/30, a speedtest from the Google hub 300/5 and a test via eg iphone 40/10.

Taking the VM box out of modem mode and connecting directly to VM gets 850/40 - perfect. wireless not as good obviously but still very acceptable.

Everything points to the Draytek (although weirdly good downloads on Google).

Anyway, that’s way OT.