The 403 error is normal and expected — the frontend app catches the 403 response and interprets it as “can’t grant admin because 2FA is required, let’s navigate to the 2FA page”.
What is not normal is:
Can you tell me where you’re seeing this error? Is it a popup in the frontend? Error in logs? As you mention, I cannot find this error message anywhere in the entire history of the codebase, so it’s very weird.