Thanks and yes, there's some progress.
I restarted the app and the the OpenID Connect Generic plugin appears to have repopulated somewhat, which is positive.
The SSO user does appear to still be missing, with only the user that came from the migration source site still present.
The SSO login button on the homepage is present since I re-enabled the SSO plugins.
I had hoped that the clouron system would be able to add the user back, though is there a path to adding the user manually?