Symptoms:
VMware vRealize Automation 8.x
As the adding of users to groups already added to the project is not considered a daily occurrence and due to the overhead of the sync its frequency is currently set on a 12-14 hour basis.
To resolve the issue and perform the sync on demand you can leverage the sync-principals API call.
Details of which can be found in the swagger API VMware Aria Automation API Programming Guide
Workaround:
Another workaround which can be performed directly in the UI is to remove and re-add the group to the project. After this any newly added users will immediately be recognized.