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When applying any changes to the SQL Server services it is advisable to do this via the SQL Server xxxx Configuration Manager to guarantee that any related permissions (files / directories / databases / instances) and policies are set correctly.



Fixing Service Accounts (Permissions and All)

We will reset all the permissions for files, directories and registry settings incl. any policies that may exist according to the requirements of the service accounts by following these quick steps.

Change the Service Accounts to Local Accounts


Open up the SQL Server 2016 Configuration Manager and navigate to the SQL Server Services branch.
In the right pane of the Configuration Manager right-click on the SQL Server service and select Properties.
In the Properties of SQL Server (InstanceName) window check that you are in the Log On tab.
Change the selector to Built-in account and select one of the three options: 


Local System 
Local Service (preferred; least privileged)
Network Service 

Press Apply and when I dialog pops up notifying you that "...any change you have made will not take effect until you reboot" click on OK.
Stop the SQL Server Service (InstanceName) 
Start the SQL Server Service (IntanceName)
Double-check the SQL Server ERRORLOG for any issues.
Repeat steps 2 to 8 for the SQL Server Agent (InstanceName) service.


Change the Service Accounts back to Group Managed Service Accounts


Open up the SQL Server 2016 Configuration Manager and navigate to the SQL Server Services branch.
In the right pane of the Configuration Manager right-click on the SQL Server service and select Properties.
In the Properties of SQL Server (InstanceName) window check that you are in the Log On tab.
Change the selector to This account and enter the details of your gMSA for the SQL Server (InstanceName) service.
Press Apply and when a dialog pops up notifying you that "...any change you have made will not take effect until you reboot" click on OK.
Stop the SQL Server Service (InstanceName) 
Start the SQL Server Service (IntanceName)
Double-check the SQL Server ERRORLOG for any issues.
Repeat steps 2 to 8 for the SQL Server Agent (InstanceName) service.




The services should now have been re-configured according to the requirements of the individual services.