I typically have no issues using the Staffing > Actions to assign roles to team members. However, there are a few requesters where I it doesn't allow me to see all team members. Help?

For the majority of my requesters, I have no issues using the Staffing > Actions to assign team members to the various roles for a project. However, there are a few requesters where it doesn't allow me to see all team members under the role. I have changed the various options including team, home group, etc. and have been unsuccessful. My workaround has been to assign the different tasks manually. Does anyone have a solution why I can't assign team members to roles using Staffing > Actions with certain requesters?