Attempting to add a new user to site w/ SAML authentication

Start with the shown create_user function, TSC.UserItem, and server.users.add call, then reproduce the SAML and ServerDefault cases against the listed Tableau Server, Python, and TSC versions. Compare the resulting permissions and user-creation behavior; done when the cause of the SAML-specific 403034 response and the expected library behavior are established.

Describe the bug
I have written a script that creates a batch of users based on json input. It works great with the exception of one caveat. My list of users only contains two users, and all users are created with SAML as their authentication method. When creating them, one of the users works fine, however one of them fails with the following error message. The user is still created, but is not created with "SAML" authentication. If I change the SAML authentication to ServerDefault, then everything works perfectly, and no exception is thrown. The only thing notable about the failing user is that every other site has the a username just like this one. This is essentially our global sso admin user.

403034: Forbidden
   	Only system administrators can add users to sites, query sites for user membership, or remove users from sites.

Versions
Details of your environment, including:

• Tableau Server version - 20204.21.0114.0916
• Python version - Python 3.9.2
• TSC library version - 0.14.0

To Reproduce
Below is my code that is handling the user creation. I only listed the portion of code that is failing and the snippet for configuring the server connection. I am calling this with an email address for the username, a basic name, and a role of 'explorer'. The server connection is configured with the new site that I am provisioning users for.

# configuration for tableau
server = TSC.Server( server_url, use_server_version=True )
tableau_auth = TSC.TableauAuth( username, password, site_name )
....
# function for creating users
def create_user( server, tableau_auth, username, full_name, user_role ):
  with server.auth.sign_in( tableau_auth ):
    try:
      # Attempt to create New User
      new_user = TSC.UserItem( username, user_role, auth_setting='SAML' )
      user_item = server.users.add( new_user )
      print( f'New User was Created: {username}'"\n" )
   ....

Results

403034: Forbidden
   	Only system administrators can add users to sites, query sites for user membership, or remove users from sites.

NOTE: Be careful not to post user names, passwords, auth tokens or any other private or sensitive information.