If your web application has dependency on the System.Net.Http Nuget package, it may break after you upgrade .NET Framework version to 4.7.2 or a newer version. This issue occurs if you are using Visual Studio 15.5 or a higher version.
Development
Web page with an iframe to a PowerApps URL keeps spinning
If a web browser starts loading the web page but it never finishes loading it, look for the resources being loaded and the debug errors in F12 Developer Tools.
If the page has an iframe, try testing the page after removing the iframe. If it works without the iframe, then look for further leads to narrow the issue down.
Sample ASP.NET page to test IIS functionality
If you want to test ASP.NET functionality in a web server, feel free to use the code below. This is the easiest way of making sure IIS can render ASPX pages.