Query on Enrol in default benefits process

Summary:

We are seeing a particular case where one employee in the organization is receiving an error on post edit formula when the "Enrol in default benefits" is run for all. This is erasing all of the employee's previous enrolments. Attaching the formula with error highlighted for reference.

There are other employees having the same elections one day prior to the QLE run who are enrolled by this process without issues. The employee in question has had previous OEs in past years with enrollments carrying over.
There has not been any employment/pesonal data changes over the past year. Would like to know what may be triggering this and ways to proceed further to resolve.