Solved Setting UI in memory on Visibility Change

I'm trying to show a certain transition UI such that when the app loses visibility and then gets back on focus, that UI will be shown to the user. It works well when I run the app from visual studio on debug, otherwise I get a flash screen of some old UI that was present in memory then the transition UI appears.
Any idea why this is happening?

Fixed it by using the window.onblur event instead of msvisibilitchange event: