surrounds out of sync

What often resolves this particular issue is a reboot of the players, particularly the main HT player (Playbase), so I would perhaps just try that to begin with.

Edit: Ensure the WiFi adapter has not been switched off on the Playbase too (if wired).

I had rebooted the surrounds. 
I will also reboot the playbase (and sub) & try again. 
 

Wireless is enabled on all, even for the ones that are wired (playbase and sub are wired). 

Is there any actual need to wire your Ones and Sub to the LAN? Those devices will normally communicate to your Playbase over an Ad-hoc 5Ghz direct (fast) wireless connection - it’s better for the surrounds to communicate directly to the main player, rather than their communication going via the wired network through your router/switch? It’s probably the latency of the wired network here that’s causing the delay/sync issues. I would personally opt to uncable the Sub & Surrounds and just leave the Playbase only wired to the LAN and see if that perhaps improves things.

OK. I disconnected the sub from Ethernet. 
I rebooted playbase/sub/surrounds. 

Only the playbase is wired now. 
Strangely enough the network matrix does not show the sub & surrounds being connected to the playbase. 
The sub connects to the upstairs beam. 
The surrounds connect to the fireplace room beam. 
Both those beams are also connected to Ethernet. 

Does the 5 GHz connection not show up on the network matrix?

I will see if the issue with the surrounds shows up again.

I believe the surrounds usually just show as being connected to an undefined 5Ghz adapter? (Not sure?) You should still see the devices in the grid though both across the top/down the side. Note: I think some of the newer Sonos devices from the Beam (gen1) onwards no longer report their status within the matrix display anyway.

The surrounds and Sub should show as being connected to an “undefined” column in the matrix.

Newer Sonos devices don’t show their Noise Floor or OFDM ANI level in the left hand column, but they do still report the Inbound/Outbound signal etc within the actual matrix.

Disconnected & reconnected the surrounds & subs again. All only connected wirelessly.

They still show up connected to beams in other rooms in the network matrix (there is no undefined column).

Music playing is still out of sync between playbase and surrounds.

If anyone from Sonos is on this thread, I created a diagnostic in the failing state (playing music with surrounds out of sync); number: 536583753

Why are they “connected to beams in other rooms”? They should only be driven via the Playbase. Or do you only mean in the matrix? 
 

When you “disconnected and reconnected” did you also power off Playbase and surrounds, then ensure Playbase was fully restarted before powering up and adding the surrounds?

Maybe a silly question, but do you definitely have them ‘bonded’ to the PlayBase as HT ‘surrounds’, rather than being ‘grouped’ with the PlayBase?

Paste a screenshot of the network matrix.