Downgrading license from Premium to Starter Keeps User as Auditor enabled which prevents LDAP login

Summary

Given a GitLab instance with a Premium license with a User with Auditor access - LDAP login is successful.

Downgrade license to Starter - LDAP login is unsuccessful.

Steps to reproduce

1. GitLab Premium license
2. User with Access level Auditor
3. LDAP enabled
4. Downgrade license to Starter

Example Project

What is the current bug behavior?

User is presented with alert message - Access denied for your LDAP account

What is the expected correct behavior?

Successful login.

Relevant logs and/or screenshots

From GitLab admin, when impersonating the User we see

{"severity":"INFO","time":"2020-08-11T23:24:45.551Z","correlation_id":"rsDWJiXOkfhn","message":"(LDAP) Error saving user ... [\"Auditor user cannot be created without the \\\"GitLab_Auditor_User\\\" addon\"]"}

Output of checks

(If you are reporting a bug on GitLab.com, write: This bug happens on GitLab.com)

Results of GitLab environment info

Detected in GitLab version 13.2.2 via customer ZD (internal use only)

Possible fixes

For each user affected, via the admin UI, change access level from Regular to Admin, then back to Regukar.