From time to time Microsoft changes their ADMX templates and that may mean a setting you have configured becomes orphaned.
Because you can not see the entry when you are EDITING the GPO you can’t delete it; you can only see it in the GPMC SETTINGS tab. So the question then becomes how to delete the rogue GPO setting?
Open a PowerShell windows as an Administrator and run the following:
Remove-GPRegistryValue -Name <NAME OF YOUR CLONED GPO> -Key "<REGISTRY PATH>" -ValueName <REGISTRY VALUE>
The REGISTRY PATH is not completely obvious. You have to prepend HKLM or HKCU depending on if it is a COMPUTER or USER policy.
The REGISTRY VALUE is the last item in the path shown.
Remove-GPRegistryValue -Name Computer-Personalization-Jun2019 -Key "HKLM\Software\Policies\Microsoft\Windows\PreviewBuilds" -ValueName EnableConfigFlighting
If you can’t figure out the value, look at the screen shot to the right.
Microsoft techs had wrongly told me, several times in the past, that it was not possible to remove such an orphaned GPO entry and that the only way around it was to rebuild the GPO from scratch.