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The newly created groups in UMS is not listed in Dashboard server after click 'Synchronize' due to you have not enabled the application access for that group in the User Management Server.
To import any user/group to Dashboard Server, you have to enable application access for those users/groups in the particular Dashboard Server application. Please refer the below help documentation link,
After providing access for the desired groups, click on the “Synchronize” button in the Dashboard Server. Now, all the groups which has access for this application will be imported to the Dashboard Server.
Please let us know, if you have any queries.