As you know, Azure App Services uses IIS or other mechanisms to run our Apps, the problem is when the Web App is not used in a determined period of time, the first petition to the web app will be slowly to load the first time, why? because the worker process that keeps the Web App running change the state to idle.
Once the Web App receive the first petition and has done this first load time, you can refresh with F5, and it will be ok again and the Web App will response inmediately.
If you’ve ever noticed this behavior an option might be to go inside of the Application Settings for the web app in the portal, and activating Always On, which keeps your web App Up and running constantly.
Keep in mind that you will not be able to turn this feature on when using the Free version of Azure App Services. It is only available in Basic or Standard plans.
Albandrod's Memory 