Build in Windows fails

I’ve upgraded Cordova-Windows to 6.0.1 recently, and for now, I cannot build.
When I build my project using
ionic cordova build windows -- --arch="x64" --phone --device --release
I get this error:

error APPX0501: Validation error. error C00CE014: App manifest validation error: The app manifest must be valid as per schema: Line 49, Column 4, 
Reason: Element '{}undefined' is 
unexpected according to content model of parent element '{}Package'. 

I see that the appxmenifest is changed to have undefined tag. But I cannot remove it since it’s added anytime I build this project.

As I said, all started to show after the upgrade.
Can I have a hint?