I have a flask web application hosted through Azure App Service that uses Azure B2C for user authentication and account management.
Upon visiting the website, a user is expected to log in using their email and password and submit a response from the user landing page.
In Azure B2C I’ve configured the sign-in user flow to return the user’s email address as part of token claims, allowing me to attach a submitted response to a particular user email.

Thus, the expected behavior in my application is: GET /login -> GET /getAToken -> GET /landing_page -> POST /submit

Problem: For about ~10% of random users , the email address is never returned as part of the token. The user would log-in using their email address and password as usual, submit the answer, yet the Web App’s logstream/ app logs would only display: GET/landing_page -> POST /submit.

Moreover, there are no traces of that user ever logging-in in the B2C tenant’s sign-in logs or traces of anyone logging-in during that particular time frame for that matter .The user’s session duration is limited to 15 min so he must log-in with email and password to access the website’s landing page.

I tried reproducing this problem by using different browsers, VPN’s, incognito mode etc, but with no success. On top of that, for a given user account, it might occur once and never occur again or might occur multiple times, despite users always using the same computer/browser setup for this exercise.

I would really appreciate any ideas on why this could be happening. Thanks!