I've noticed this issue when working on a secondary Monitor. Here's the two Monitor with different resolution and Scaling:

When I launch the App in Monitor 1, the BusyWindow is positioned correctly:

If I hit Windows + P and select Extend, and move the app to Monitor 2, it also works fine on the Monitor 2:

If I hit Windows + P and select Second screen only, run the app and hit refresh buttons, the BusyWindow opens in wrong position or goes off screen:

How to fix this problem?
EDIT
Looks like the problem is with scaling! I didn't have App.config and app.manifest files in my project, I have added those 2 with following content in App.config:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<runtime>
<AppContextSwitchOverrides value ="Switch.System.Windows.DoNotScaleForDpiChanges=false"/>
</runtime>
</configuration>
and app.manifest:
<?xml version="1.0" encoding="utf-8"?>
<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
<assemblyIdentity version="1.0.0.0" name="MyApplication.app"/>
<trustInfo xmlns="urn:schemas-microsoft-com:asm.v2">
<security>
<requestedPrivileges xmlns="urn:schemas-microsoft-com:asm.v3">
<requestedExecutionLevel level="asInvoker" uiAccess="false" />
</requestedPrivileges>
</security>
</trustInfo>
<compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
<application>
</application>
</compatibility>
<application xmlns="urn:schemas-microsoft-com:asm.v3">
<windowsSettings>
<dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true</dpiAware>
<dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitor</dpiAwareness>
<longPathAware xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">true</longPathAware>
</windowsSettings>
</application>
</assembly>
and my Windows 10 is Version 1809 (OS Build 17763.1999), with all those in project and 125% scaling in Monitor 1, this is what it does:



