I found the issue, I was only searching under the active filter. I removed it and found this user has been deactivated. I know what to do from here. Thank you. 

I searched the email and also went back to see if I could find the actual persons name with no luck. 

I am trying to add a new user however when I submit I get an error stating that the username is already taken. When I try to search the user it does not exist and when I try to assign a task to this user it cannot find them. How can I fix this?