When the non-GIS Professional user types with add-on ArcGIS Pro licenses are migrated to GIS Professional user types, ArcGIS Pro or ArcGIS Online returns errors on ArcGIS Pro licensing. Licenses are no longer available to revoke.
If the number of affected users is small, reach out to the Customer Service Representative of the subscription to temporarily add back any ArcGIS Pro add-on licenses and non-GIS Professional user type spaces removed. Then move the user(s) to the non-GIS Professional user type, revoke the license, then move the user(s) back to the GIS Professional user type.
If a large number of users are affected, log a Tech Assist to work with ArcGIS Online tech lead to modify the licensing behind the scenes with the help of the Development team. However, this takes some time to complete.