Created attachment 15727 [details]
Reproduction of stated issue
The Appearing event (and OnAppearing) does not fire for a Tabbed Page or Master Detail page if that page has previously been displayed. The event only fires the first time the page is displayed. Content Page will fire correctly each time the page is displayed.
Attached is a reproduction that displays an Alert as part of the Appearing Event. On the root page a button that loads Content Page, Tabbed Page and Master Detail Page. Each time the Content Page appears the alert is shown, but only the first time the Tabbed Page is shown does this happen.
Should be fixed in 2.3.4-pre1. Thank you!
I have checked this issue with Xamarin.Forms 2.3.4-pre1 and observed that this issue has been fixed.
Hence closing this issue.