'End user getting "Missing required element [Email Address]" error on Forcing password reset first logon

We are following Azure B2C sample code Azure AD B2C: Force password reset first logon to implement logic to force new local user to reset the password on the first login since we don't want them to use temporary password we generated for them. It has been working good for us, however recently one of such end users got this error "Missing required element [Email Address]" during reset screen:

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We have been tried to reproduce this and we could not. We are not sure how to investigate this further at this point. Could someone shed some lights on this issue?



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