Why IDCS/IAM Group and members got deleted and add back in audit logs for FCCS?

Summary:

In all EPM cloud application (Eg. FCCS) for Audit logs IDCS/IAM Groups and Group members(users) got deleted and add back.
It's getting deleted by System at the time of daily Maintenace but add back again after 3-4 hours.
for example, it's getting deleted at time of 4:35AM IST. adding back again 8:30AM sometime 9:30AM IST as per Audit logs.

We have couple of question:
1. Why IDCS/IAM user/groups deleting and adding back?
2. Once Users and group deleted before adding back user/groups, can any user login to applications??
3. Why Adding back to group after long time?