Intermittent issues with Azure WebApp constantly stop functioning, a Stop/Start operation brings it back online.
Further investigation using Azure Application Insights, reveals the Azure WebApp was experiencing a few FailedRequestCount, with HTTP 500 Errors. An exception was thrown by a TaskScheduler. Exception of type ‘System.OutOfMemoryException’ was thrown.
In my case, the service that was running on the Azure WebApp was using .NET Core 2.0, the fix was to upgrade to the latest version.
.NET Core 2.0 is an unsupported version and we highly recommend upgrading to the latest version (3.1). Please take a look at this information of the .NET Core official support policy: https://dotnet.microsoft.com/platform/support/policy/dotnet-core
For .NET Core applications I suggest enabling the stdout logs, as those will capture some important errors: https://learn.microsoft.com/en-us/aspnet/core/test/troubleshoot-azure-iis?view=aspnetcore-2.2#aspnet-core-module-stdout-log-azure-app-service-1
If those OutOfMemory exceptions come with a 5xx status code, I would suggest as well using the AutoHeal feature as it will allow setting rules based on that status code to capture a Memory Dump, you can check more information here: https://azure.github.io/AppService/2018/09/10/Announcing-the-New-Auto-Healing-Experience-in-App-Service-Diagnostics.html