If you've changed the leaving date multiple times, the system reruns the calculation of the remaining holiday each time the final employment date is changed, meaning it doesn't start the calculation from scratch.
In the employee's planner settings, check the history of the entitlement and amend their entitlement to what it was before using the leaver wizard.
📌Note: The entitlement displayed in the leaver calculator is the employee's normal holiday entitlement, without any TOIL or carryover. The system deducts any TOIL booked from the TOIL entitlement if the TOIL booked is before the leaving date.