Hi there,
Check your Azure AD connect sync scheduler. By default every 30 minutes a synchronization cycle is run. If you have modified the synchronization cycle you will need to make sure that a synchronization cycle is run at least once every 7 days.
Azure AD Connect sync synchronizes changes occurring in your on-premises directory using a scheduler. There are two scheduler processes, one for password sync and another for object/attribute sync and maintenance tasks.
Azure AD Connect sync: Scheduler
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