Application Initialization *stops* working for .NET Core

### Describe the bug
Per https://github.com/dotnet/aspnetcore/issues/3849 and https://github.com/dotnet/AspNetCore.Docs/issues/16675, there are scenarios when App Init stops working entirely for .NET Core processes.

Warmup.dll is loaded into IIS, and attempts to look for an endpoint at the website (e.g. if I tell it the preload URL is (site)/start, ProcMon reveals warmup searching for (Websitefolder)/start), but fails.

My intention is to run background tasks within the same .NET Core MVC project, which helps *enormously* with code consolidation, while maintaining responsibility separation.

### To Reproduce
Reproduction is difficult. I have several servers in which this behavior occurs, but it appears to only start happening after some period of time (publishing to the endpoint many times, Windows Updates in between, etc.).

Reinstalling IIS and registering App Init/.NET Core modules temporarily resolves the issue.

### Further technical details
I don't know what is needed to proceed - I can provide details of places where this continues to fail.

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Current Workaround: Run some out-of-proc task to run any harmless MVC min at X frequency - this starts the dotnet process as expected. (e.g. Scheduled Task that sends a request for (WEBSITE)\start every 5min)