After trying to reset the write scope setting back, please wait or force the AD synchronization. You can use the following command to check the CustomRecipientWriteScope again:
Get-ManagementRoleAssignment -RoleAssignee "Organization Management" | export-csv c:\location\Get-MgmtRA-OrgMgmt.csv
For your reference: Restore Organization Management Role Back to Default Settings.
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What errors do you get when remove a role from the role group?
What about removing the unwanted role with EMS? Try this command, if you still cannot manage roles for Organization Management role group, you can post the screenshot here and don't forget to cover your personal information:
get-ManagementRoleAssignment "Mailbox Search-Organization Management" get-ManagementRoleAssignment "Mailbox Search-Organization Management"|Remove-ManagementRoleAssignment
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