Flask session not persistent across requests in Flask app with Gunicorn on Heroku

Looks like there were two problems:

• The app.secret_key shouldn't be set to os.urandom(24) because every worker will have another secret key
• For some reason the dict where I stored my sessions in was sometimes empty and sometimes not... Still haven't found the reason for this though

Storing the sessions in a database instead a dictionary at runtime solves the problem.