What triggers or hooks an employee for the Update Accrual Plan Enrollment process?

Summary:

Employee's accrual plan is end-date and then re-enrolled in the same plan. There are no changes to the employee's assignment.

Why is it doing this?

Content (required):

I read documentation and opened an SR - which advised me to post the question here.

1. Eligibility profile criteria is based on assignment, like Business Unit or assignment category.
2. Profile Usage = Benefit because Absence isn't on the drop down.
3. Enrollment Start and End Date is derived through a fast formula.

The Update Accrual Plan Enrollment process runs every night with an effective date = SYSDATE. Employee has had no changes in their assignment. There might have been a benefit or compensation change but those attributes are not used to determine accrual plan eligibility. The process ends and re-enrolls the employee for the same plan. Why does it do this? See example below.