WMS - Employees Disappear From Resource List Of Employees

 We have three employees that are disappearing from one particular resource on a daily basis.  There does not appear to be any particular uniqueness that is shared by the three users.  

Each day they discover that they cannot transact tasks, and each day it is discovered that they are not on the list of employees assigned to that resource.  They are reassigned to the resource and functionality returns to normal.

Navigation: Warehouse Manager>Resources>Employees

I'm looking for any process that may be running that might cause this.  Does anyone know of a process that would remove an employee from a resource employee assignment?