Thanks for the reply.
Already in contact with Support, slight change, uninstallation of ESET Mobile Security from the test client's Android Personal Profile may have had an impact. I can now see that the client device is using an old certificate, the MDMCore.msi was reinstalled with the correct new certificate but seems to have rolled back to an old certificate. Could this be the recycled SQL database?
Current MDM Connector status has the alert "HTTPS certificate change still in progress. The old certificate is still being used" and the newly registered (but not properly enrol