Why can user not sign up through Microsoft Entra Id sign in and sign up user flow?

Marc Rufer
120
Reputation points MVP
We set up a sign up and sign in user flow in Microsoft Entra Id for external identities. Users of Tenant A could successfully sign up. However one user couldn't. When trying to login, the user gets the error, that Account does not exist in tenant. After clicking in create new, the user gets the MFA challenge of tenant A but after successful MFA he gets then redirected to the before mentioned login page with the error message that the account dies not exist in the tenant.
No guest user got created and I could not find any details in the logs.
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