Hello,

After further investigating this we decided to decline the report. The reason behind this decision is the default behavior of the Visual Studio's XAML Designer. Basically, the designer is dealing with actual types and assemblies and this combined with the fact that Visual Studio is a 32-bit process some of those types cannot be activated from ARM and x64 binaries. 

To work this around switch to x86 while using the XAML designer.

https://social.msdn.microsoft.com/Forums/en-US/eab4fc3c-a77d-41d6-b3dd-48f636d70035/design-view-is-unavailable-for-x64-and-arm-target-platforms?forum=toolsforwinapps

Regards,
Martin Ivanov
Technical Support Engineer