Thank you very much amiga-dude for your prompt response and helpful suggestions.
The details of my network adaptors (I am using a Microsoft Surfbook 2) are:
- Marvell AVASTAR Wireless-AC Network Controller
- TAP-Windows Adapter V9
I am afraid I do not immediately have the motherboard model.
As the Ubuntu was using the same ethernet connection (and adapters for that matter) and getting 887, I do not think those would be the problem.
I was running Ubunto off a stick

Thank you very much jimbof for your prompt response and helpful suggestions.
I had never heard of Hamachi and have looked it up.
I last used Logmein before I had the current PC so I think I am clear of that. But, as you say, there may be other problems caused in a similar way.
However my other W10 PC is newer and has not done anything exciting in its life but it still has the same problems.
I did look at altering W10 power management settings but, as it all seemed to be a question of degree, I could not see the point. Again the newer PC has the same problem – but with different settings as it is a desktop.
I have asked Zen to be more specific about their advice and wait hearing from them.
On the subject of VPNs’, Bitdefender has come out with one which is not a slower connection.

Well, if you know how to open an administrator command prompt, you could do worse than checking that >something< hasn't set those options to a sub-optimal state.

From administrator command prompt:

netsh interface tcp show global

Out of interest, what ethernet interface are you using that doesn't have the "large send offload" options?

In reply to a post by JMaples:

Yes, I do have both Bitdefender and Malwarebytes running but saw no change when I switched both off.

Switching off doesn't remove their software from deep in the internals of Windows. It just stops it flagging if it finds something they don't like. For this test you have to uninstall and reboot.

Make sure you note down any licence keys for any subscriptions.

In reply to a post by JMaples:

The details of my network adaptors (I am using a Microsoft Surfbook 2) are:
- Marvell AVASTAR Wireless-AC Network Controller
- TAP-Windows Adapter V9

Do you mean "Surface Book 2"? That doesn't even have a wired ethernet connector AFAICS. "TAP" is a virtual interface only.

You're very unlikely to reach gigabit speeds over wireless, despite what manufacturers' numbers say. You *might* on certain very carefully tuned configurations of 802.11ac - if both AP and laptop support MIMO and are configured for 80/160MHz channels. See wikipedia.

In my setup with Unifi AC Lite and Macbook Pro 2015 13", I have a theoretical "peak" 867Mbps, but that translates to about 400-450Mbps throughput in practice (when talking via wireless to a local wired server).

In reply to a post by candlerb:

Do you mean "Surface Book 2"? That doesn't even have a wired ethernet connector AFAICS.

To get one you need the Surface Dock which connects to the propitiatory Surface Port on the side. This is then a full GigE connector.

Alternatively a USB-C 3.1 to Ethernet adaptor may work at the higher speeds.

Am using a 100 Meg FTTP connection but want to try and help if I can.

I actually get about 108-110 down myself, switch off energy efficient Ethernet as advised.

It may well be worth seeing if there's a NIC driver update but I'd imagine Zen will have explored this themselves.

If you access the properties for your wired LAN connection, it does indicate it's connected at 1 Gbps doesn't it?

Ultimately it's down to MS to fix, make sure you have all cumulative updates installed.

OP said "...and can log (by wire to the router) 887 with Ubuntu but only about 300 with Windows 10"

887Mbps down is about 94% of possible GbE throughput and near enough the rated FTTP service speed. It has to be wired.

Thanks jimbof.
I ran “netsh interface tcp show global” and found that “Receive side scaling” was “enabled” and “Receive window autotuning” was “normal”.
The ethernet adapter is TAP-Windows Adapter V9

Tx. I have sent support requests to both firms.