Firebase Auth: A user (email) logged using signInWithEmailAndPassword, won't work with signInWithRedirect - firebase-authentication

Question

I'm building a Web application that uses Google Identity Platform to authenticate users.
All users belong to an Azure AD Domain, which is connected to Google Identity Platform through the use of an OIDC Provider, as per documentation.
Code wise, the authentication is performed using Firebase JS SDK (9.6.11).
When the application starts, there is no OIDC Provider to the Azure AD Domain (mydomain.com).
This configuration is created within the web application.
As there is no OIDC Provider to the Azure AD Domain, no user can yet login.
As such, in order to configure the Azure AD settings in the Web application, a temporary user is created in Goggle Identity Platform, so the User can login into the Web application:
Once the user is created, the user **is now able to login, **, using the password set on Google Identity.
Once the Azure AD Settings are configured, the Web application:
DELETES the temporary user from Google Identity,
Creates an OIDC Provider on Google Identity, connected to the configured Azure AD Domain (see image as an example of the OIDC Provider settings that the app would create):
The above provider is used to login users from Azure AD (mydomain.com), using the signInWithRedirect function, as per the documentation.
import { getAuth, signInWithRedirect, getRedirectResult } from "firebase/auth";
const auth = getAuth();
const provider = new OAuthProvider("MyDomainTenantID");
provider.setCustomParameters({
login_hint: user,
});
signInWithRedirect(auth, provider);
getRedirectResult(auth)
.then((result) => {
// User is signed in.
});
After configuring the Azure AD OIDC provider, all the Azure AD users (mydomain.com) are now able to log in into the Web application, EXCEPT the user that was used as the temporary user.
In the above example, myuser#mydomain.com, is not able to Log In into the Web application through the same Azure AD OIDC provider.
Please note, that the user no longer exists on Google Identity, as it was removed, so it can be logged in through the Azure AD OIDC provider, and recreated by the JIT process on a successful login.
Analyzing the Console, the call to https://www.googleapis.com/identitytoolkit/v3/relyingparty/createAuthUri fails with a 400 Error: Firebase: Error (auth/operation-not-allowed)
The POST Request body:
{
"providerId": "MyDomainTenantID",
"continueUri": "https://xxx.firebaseapp.com/__/auth/handler",
"customParameter": {
"login_hint": "myuser#mydomain.com"
},
"tenantId": "GoogleIdentityTenantId"
}
As mentioned, ALL users from the same Azure AD are able to login, EXCEPT the one that was initially used as an Email/Password user.
According to Firebase documentation, the auth/operation-not-allowed error occurs when:
The provided sign-in provider is disabled for your Firebase project. Enable it from the Sign-in Method section of the Firebase console.
BUT, this is not the case:
The OIDC provider connected to Azure AD is enabled
All the users from the Azure AD Domain (except myuser#mydomain.com), can successfully login.
I followed all the guidelines from Firebase, and i can't understand why that specific user is not being able to login.