The issue arises because the in-process hosting model for ASP.NET Core applications in IIS does not currently support the IIS Application Initialization module as expected. This limitation is referenced in the issue you linked https://github.com/dotnet/aspnetcore/issues/8057 In this hosting model, the IIS worker process (w3wp.exe) directly hosts the application, and requests may not reach the initialization endpoint as desired during startup or slot swaps. For more information and review links shared https://techcommunity.microsoft.com/blog/iis-support-blog/application-initialization-in-iis/4232177 https://learn.microsoft.com/en-us/aspnet/core/host-and-deploy/iis/in-process-hosting?view=aspnetcore-9.0