In the Client List in TaxSlayer ProWeb, whether a preparer sees the first five digits of taxpayer SSNs masked or unmasked is determined by a setting in the Role they have been assigned. If a preparer hasn't been assigned a Role, then they will see SSNs unmasked in the Client List.
If you're not familiar with creating or assigning Roles in TaxSlayer ProWeb, see here to learn about Roles.
In the Role you assign to a preparer, if you wish for the SSNs to be masked in the Client List be sure to uncheck the permission to view the full SSN:
View Full SSN