Why *.appinstaller corrupts my UWP install ONLY on Windows Update 1809

I have a UWP app that has been working fine until the latest Windows Update (1809).

If you install the app from the .appxbundle file (from Additional Links->Package Bundle on the index.html page that is created with the app package), everything works and the app launches with no errors.

If you install the app from the .appinstaller file, it installs with no errors but the app crashes on launch with the following error in Event Viewer:

Faulting application name: ClaimsTool.UWP.exe, version: 1.0.0.0, time stamp: 0x5c889177 Faulting module name: ntdll.dll, version: 10.0.17763.404, time stamp: 0xbf6ea104 Exception code: 0xc0000005 Fault offset: 0x000000000004df23 Faulting process id: 0x4d60 Faulting application start time: 0x01d50071ab8b5170 Faulting module path: C:\WINDOWS\SYSTEM32\ntdll.dll

When I run the App on a machine that does not have the 1809 update, it works with no errors. Any ideas?

Why does my app crash on launch ONLY when installed from the .appinstaller file ONLY on Windows Update 1809?

The app has been rebuilt multiple times, with and without the .NET native toolchain, making sure to target the correct Windows versions. No dice.

EDIT 1: For testing, I've purposefully put the wrong mime-types in IIS. When IIS has the wrong mime-types, the installer fails. When the mime types are correct, the installer works but the app crashes on launch.

EDIT 2: I found 2 pages from MS that list conflicting mime-types for .appx, .appinstaller and .appxbundle files.

1. This Microsoft page, suggested by @NicoZhu-MSFT, lists the following mime-types:

.appinstaller file, available as an application/xml

.appx and .appxbundle files, available as application/vns.ms-appx

2. This Microsoft page, which I found while troubleshooting, lists the following

fileExtension=".appx" mimeType="application/appx"

fileExtension=".msix" mimeType="application/msix"

fileExtension=".appxbundle" mimeType="application/appxbundle"

fileExtension=".msixbundle" mimeType="application/msixbundle"

fileExtension=".appinstaller" mimeType="application/appinstaller"

Notice that all three mime types for appx, appxbundle and appinstaller are different. Unfortunately, neither page's mime types fix the problem on Windows 1809, and both sets of mime types work on earlier versions of Windows 10.