It is possible that some workers do not appear in the list of employees and that, when trying to create them, the message "Duplicate primary password (Tax ID Employee). Enter a new one" appears.
This means that the employee is already created for this company but you may not see it for the following reasons:
You are applying a Contractor and/or Work Center filter and that employee is not assigned to that Contractor or Center for which you are filtering. In this case, make sure that you are not applying any filters in the dropdowns on the left:
The worker may be on leave for the current date (you can see this more clearly in this video) or may not be assigned to any center. In this case, you just have to uncheck the "See only assets" check and check "See all" and you will see all your employees.