As of this writing, when HTTP module is enabled, the warming HTML page defined in AppInt module may not load properly. Good news is, there is a workaround which is to place the managed module onto the GAC to have the warming page shown correctly.
FYI, for the right testing, you need to recycle IIS apppool first.
Here is how you can make a test/sample managed-module and place it in the GAC (code sample is placed at the end of this blog).
Build MyIIS7Procject.dll from the Developer Command Prompt for VS 2019