Hello Seamus,
Small world that it is, I was just about to write a response to your question when a call came in to vSAN GSS and it was yourself!
Posting how we fixed it here to benefit anyone else that finds this post while encountering something similar.
So, in the vSphere Client multiple tabs relating to vSAN information were missing (vSAN Health, Performance, Disk Management etc.), these all rely on the vmware-vsan-health service running on the vCenter managing the cluster.
In your case you noted that this was in an impaired state and you restarted this service - we validated that it was actually running in that we could see current vSAN Health query jobs returning output for the tests.
This indicated that one of the services that vmware-vsan-health relies on to display data in the vSphere Client was impaired (e.g. vsphere-client service), simply stopping all vCenter services and restarting them resolved the issue - it is generally advised to do it this way if possible as then we can ensure services are restarted in the right order bearing in mind their dependencies etc. .
Bob
