In Redwood Change Working Hour FTE is not calculating appropriately upon changing worker hours

Redwood -In change working hour page FTE value doesn't update automatically when the working hours are changed, the page is exhibiting inconsistent behavior with FTE logic working in some cases and not in others.

Background: Default Assignment category based on the certain conditions.

Business Rule: As per requirement we have written multiple business rules such that assignment category changes up on changing the working hours.

Issue: Assignment category is working absolutely fine; but some times when we give edge working hours like 39 and 59 FTE is not calculating.

Requirement:

EMP

Working Hours	Assignment Category
>= 60	Full-Time Regular
>=40 and < = 59	Part Time Regular
>= 1 and < = 39