XamlParseException on RS4 & RS5

Describe the bug App crashes on some users machines, crash reports coming from AppCenter:

One device running 10.0.17134 Windows.UI.Xaml.Markup.XamlParseException: The text associated with this error code could not be found. Cannot locate resource from 'ms-appx://Microsoft.UI.Xaml.2.4/Microsoft.UI.Xaml/Themes/rs4_themeresources.xaml [Line: 0 Position: 0]

Another one running 10.0.1776: Windows.UI.Xaml.Markup.XamlParseException: The text associated with this error code could not be found. Cannot locate resource from 'ms-appx://Microsoft.UI.Xaml.2.4/Microsoft.UI.Xaml/Themes/rs5_themeresources.xaml'. [Line: 0 Position: 0]

I am only using <XamlControlsResources xmlns="using:Microsoft.UI.Xaml.Controls" /> in my App.xml and muxc:NavigationView from the WinUI library

NuGet package version: Microsoft.UI.Xaml 2.4.0

Windows 10 version	Saw the problem?
Insider Build (xxxxx)	No
November 2019 Update (18363)	No
May 2019 Update (18362)	No
October 2018 Update (17763)	Yes
April 2018 Update (17134)	Yes
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Mobile
Xbox
Surface Hub
IoT

[kmahone]

I’ve filed a separate issue for the ‘CalendarDatePickerTopHeaderMargin’ issue: #2719 RS4 and lower: Cannot find a Resource with the Name/Key CalendarDatePickerTopHeaderMargin

Fixing this in WinUI should be pretty straight forward.

If you want to work-around this issue in your app until we have a release out containing the fix, it should be easy. Just add this Xaml to your App.xaml: <Thickness x:Key="CalendarDatePickerTopHeaderMargin">0,0,0,4</Thickness>

The cause of the other issues is still unclear.

In AppCenter, do you have the ability to see the full call stack of the crash? Or do you just see the error message? (I’ve personally never used AppCenter).

[tipa]

Bumping this (see https://github.com/microsoft/microsoft-ui-xaml/discussions/8638).