Background: As previously announced here - Azure App Service will get support for .NET 4.7 by the end of June 2017. Recently we have seen instances where web apps started failing with below symptom as a result of .NET Framework 4.7 updates. If your Azure App Service is affected by below symptom, please follow below recommendations.
Symptoms: Sitefinity based ASP.NET Azure App Service might not work as expected and could fail with System.TypeInitializationException exception or with error “The type initializer for 'Telerik.Sitefinity.Security.SecurityManager' threw an exception.”
Cause: This problem occurs when there is a complex nested Sitefinity custom membership provider integration causing the apps to break and raise the exception. So far this symptom has been observed only with Sitefinity based ASP.NET web apps leading to app failure. We are not aware of any other ASP.NET web apps having such issue.
Solution: Because majority of the reports are around Sitefinity based ASP.NET web apps, to address above problem Sitefinity has suggested to follow below recommendations and install Sitefinity hotfix to deploy it to Azure App Service: