VCSA 6.5 Web GUI Error

I have successfully upgraded my VCSA 6 to 6.5 - after the upgrade I was able to login and use the vsphere web client without issue.

I then upgraded my single ESXi 6 host to 6.5, which was successful.  After booting up the VCSA, after logging into the Vsphere client I get the following error:-

Could not connect to one or more vCenter Server systems:

https://FQDN:443/sdk

At this point the client is unusable.  I have tried stopping and restarting all services via SSH, and rebooting the VCSA, however nothing has helped.

I have also tried following the instructions here “Failed to verify the SSL certificate for one or more vCenter Server Systems” error in the vSphere Web Client (2050273) … - However I only see 1 Service ID, so there doesn't appear to be a duplicate entry..

Many thanks