This is usually caused by the agent/employee profile not being active. To check this, login to your website administration and do the following steps:
Click on Employees & Locations or Agents & Offices.
Now select, View Agents or View Employees.
Find the agent that is not appearing on the website.
Click the option, Edit.
Ensure the "Display on Website" checkbox is checked.
Click, Next Step.
Click, Skip this Step.
Check your website to see if the profile displays.