If a web app pool has a private bytes limit, and .Net Framework upgraded to 4.7.2, the web app will be down when the w3wp.exe approaching to the private bytes limit. An App_Code.dll.Delete (or other .Delete) file is created in ASP.Net temp folder at runtime when the w3wp.exe process memory approaching to the set Private bytes limit. And because the .Delete file exists, the assembly cannot be loaded and that will cause the web app down.
The current workaround is to remove the Private bytes limit, and manually clean the .Delete file under the ASP.Net temp folder. The issue will be addressed in the next release of .Net Framework.