After upgrading HMOL to v6.1r3 I have lost an Administrator's account after the database transfer. When I try to recreate it, an error is thrown saying the account already exists. How to I recover this "missing" account?
The administrator table may have been lost in the upgrade procedure to the new VHM. I have not seen this occur in the past but it is certainly possible.
The error displayed stating that the administrator is already in use is likely due to the fact that the administrator is still present in the previous standby (backup) version of your VHM.
I would recommend rolling back the Hivemanager to the previous standby version and then attempting the upgrade again. Considering we haven't seen something like this occur, I find it highly unlikely it would occur twice in a row on an upgrade procedure for you.
You can roll back HiveManager to the previous version using the option under Home > Administration > HiveManager Operations > Revert Software Version. Think of this like a secondary partition within our cloud that will be in the same state it was when you started the upgrade procedure, and then follow the normal upgrade process to try again.