Sitecore instances hosted on Windows Server 2012 R2 can suffer from unexpected application shutdowns. The shutdown occurs due to numerous file changes to the \App_Data folder. In the log files, you can see the following warning:
WARN Shutdown message: Directory rename change notification for 'C:\inetpub\wwwroot\mySite'.
Overwhelming Change Notification in mySite
HostingEnvironment initiated shutdown
The issue is caused by the following known issue in Windows Server 2012 R2 OS: https://support.microsoft.com/en-us/help/3052480/unexpected-asp-net-application-shutdown-after-many-app-data-file-chang.
As a permanent fix, implement one of the resolution methods suggested by Microsoft in the aforementioned article.
As a workaround, disable the \App_Config\Include\Sitecore.Diagnostics.config file by renaming it to Sitecore.Diagnostics.config.disabled.
This file configures a collection of diagnostics information that can be useful to troubleshoot Sitecore behavior. It also enables configuration files dump functionality. It can be safely disabled if there are no ongoing troubleshooting processes that require enabled diagnostics. However, since the .config file dumps will no longer be created, you must ensure that the solution is regularly backed up.