MarkdownTextBox does not show complete MD Text

Describe the bug

A clear and concise description of what the bug is. I bind a markdown string to the MarkdownTextBox, however on some strings, the textbox only shows some parts of the string (e.g. the last part). The string is loaded from my github project's latest release changelog. When I debug the app, the string is completely downloaded, the bug must occur inside of the markdown textbox.

• Is this bug a regression in the toolkit? If so, what toolkit version did you last see it work:

Steps to Reproduce

Having a MarkdownBox: <controls:MarkdownTextBlock Text="{Binding Changelog}" FontSize="14" Background="{StaticResource BackgroundColor}" Foreground="{StaticResource UIForeground}"/>

Binding the following markdown string (see here): "**Important: With this version, the required OS build is changed to Windows 10 / Windows 10 IoT Core - Build 1903**\r\n- Added new Settings for Bots (Autocorrect Order Time/Amount)\r\n- Added the possibility to reset Bot Statistics, also available as Telegram Command (Use this, if you traded manually while a Bot on the same Trading Pair was active)\r\n- The Candle Chart in Backtest View is now detachable, so you can use multi-monitor setups"

Expected behavior

Complete appeareance of the binded string

Screenshots

If applicable, add screenshots to help explain your problem. https://imgur.com/a/dEBEK6a

Environment

NuGet Package(s): Microsoft.Toolkit.Uwp.UI.Controls

Package Version(s): 6.0.0

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [x] October 2019 Update (13363)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [x] May 2019 Update (18362)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [x] IoT

Visual Studio 
- [ ] 2017 (version: )
- [x] 2019 (version: 16.5.4 ) 
- [ ] 2019 Preview (version: )

Additional context

Add any other context about the problem here.