Python Flask on Windows IIS - Expert (dev-ops) -- 2

I am running a Flask app on a windows server. The developer says the code works perfectly on his local computer (which is linux) But when we move it to IIS server we have issues: below is a snippet of the issue. And attached discussed the flow of the app (look at page 1-3) issue: We use flask-session of type 'filesystem' to manage our cookies. When a user has been signed up, we store his data in db ('pbi_users') and retrieve the id of the created record. This id we put in session object (in cookies). It works for the first call of the dashboard page (welcome message). However, it vanishes on the second call for dashboard.