I am no longer the WorkGroup Administrator for our Certificate Licenses
You are the WorkGroup Administrator for certificate licenses, and you are suddenly no longer able to add and remove members.
You lost the administrator privileges because you created a join code that revoked these privileges.
When you create a join code, if the "Admin" checkbox is not selected (under "Advanced Options"), and you then apply that join code to yourself, you will effectively rejoin that workgoup without the administrator privileges.
Contact our Sales Desk (firstname.lastname@example.org), and request that your privileges be restored.