Flask get request have inconsistent return

I used flask to build a mini server on heroku. The server side code looks something like this:

    from flask import Flask
    from flask_cors import CORS, cross_origin

    app = Flask(__name__)

    schedule = {'Basketball': 'old value'}

    @app.route("/")
    @cross_origin()
    def get_all_schedule():
        return json.dumps(schedule)

    @app.route("/update", method=['post'])
    def update_basketball_schedule():
          globle schedule
          schedule['Basketball'] = 'new value'

    if __name__ == "__main__":
        app.run(host='0.0.0.0')

I have one global dictionary 'schedule' to store the schedule data. I use the post url to update this schedule, and use the "/" url to get the data, seems pretty straight forward.

I am testing this application on my Chrome browser. I called the post url once. And then When I calling "/", sometimes it returns the dictionary with "new value" and sometimes it returns the the dictionary with "old value". What is the reason for this behavior?

I am using a free dyno on heroku. in my Procfile:

     web: gunicorn server:app