We have installed the probe and configured the user Sync from on-prem AD, all were fine till last month.

However, when the employee’s manager details changed in AD is not getting updated in Freshservice though sync is happening (email address changes are visible). Also noticed that sometimes users get deactivated.

This is impacting the Service Request approvals workflow.

any idea, how can we address this? 

In the past similar issue happened and we did remove the Probe and configured everything from scratch, perhaps, it caused user login and other sort of issues.