can you check the employee ids which are not getting payment date.
check with HR team, how they are maintained those employee data.
As my guess missing payment date empoyee data may be maintained by different way than asusual.
Try to compare the emplyee data which is not getting payment with other employee which getting payment into bw loads.
by seeing whole record information you may find the difference.
if user maintained the employee in standard way then only only your logic will work.