– First, you need to make sure that you have enable App Insights in your App Service
– Check the application insights log:
– Login to Azure, got to your App Service
– Click on SSH on the left,
– Check the application insights start up log in this folder: /var/log/applicationinsights
– View 2 logs file there, it will give you some hint what could be wrong.

There are some common issue:
– Wrong instrumentation key
– Application has already instrumented application insights in their code, that means it will not use the App Insights agent by the server. In this case you need to have a way to make sure that your Application Insights code pickup the right instrumentation key.