We are following post below for the steps to configure ApplicationInsights and also have applied the patch as specified in the article. After setting things we are getting a NullReferenceException (details below). We have verified, all steps were followed as per

Any suggestions on what could be the issue or next steps to troubleshoot this?

Article Azure Application Insights not working on Sitecore 9.1 PaaS

Also from blog at - https://sitecoresysadmin.wordpress.com/2019/04/05/solved-application-insights-not-working-on-sitecore-9-1-paas/

Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

[NullReferenceException: Object reference not set to an instance of an object.] Sitecore.Cloud.ApplicationInsights.TelemertyInitializers.AppInsightsInitializer.Process(PipelineArgs args) +74