VB6 With XAML Sample: toast always create a new instance of app instead of resume the existing app

[Tan2NT]

Hello,
I run this app: https://www.microsoft.com/vi-vn/p/vb6-app-with-xaml-sample/9n191ncxf2f6?rtc=1&activetab=pivot:overviewtab
to generate toast notification. Then I click on the notification, but it launches a new instance of the app instead of resuming from then existing app.
Could you please let me know why it happened? and how to fix this?
I want to integrate push notification into my Desktop bridge app and have the same problem.

Thank in advise!