windows 10 - Hyper-v - Virtual Machine could not be started because the hypervisor is not running ... But it is

I've seen various threads on this subject but none of them solve the issue I have. I want to be able to run Docker for Windows on this machine but even though it installs i get a problem at start up. The problem appears to be nothing to do with Docker, as no VM will start.

For reference, I did successfully run Hyper-v when I first got the machine (late 18) and ran Docker for Windows OK. But I had to go back to VirtualBox for a while and now that I can go back to hyper-v I find I get the problem.

Machine is a Lenovo Thinkpad P51 with 32GB memory, running Windows 10

bcdedit reports:

hypervisorlaunchtype    Auto

systeminfo reports:

Hyper-V Requirements:      VM Monitor Mode Extensions: Yes
                           Virtualization Enabled In Firmware: Yes
                           Second Level Address Translation: Yes
                           Data Execution Prevention Available: Yes

The services - I think this is correct:

The Windows features show as installed:

Where am I going wrong ? Any other logs/messages that i can look at ?

FWIW - I can disable Hyper-V and run VirtualBox without any issues....