In iOS, an ActivityIndicator, which is a ViewCell in a ListView, disappears when scrolling. When the ViewCell moves off the visible screen area and back in during scrolling, the indicator is no longer visible.
This has been reported before: https://forums.xamarin.com/discussion/62974/activityindicator-disappears-while-scrolling-in-the-listview
I have made a test project which shows this behaviour: https://github.com/KolibriDev/TestLayoutXaml
Note that this is only a problem in iOS - works in Droid and UWP.
I can confirm this issue.
At the moment, I can't figure out what's causing this. A workaround seems to be setting IsRunning to false and then true. Add this to GetCell of ListViewRenderer:
if ((cell as ViewCell).View is ActivityIndicator)
((cell as ViewCell).View as ActivityIndicator).IsRunning = false;
((cell as ViewCell).View as ActivityIndicator).IsRunning = true;
Of course, this is not even a hack. If the activity indicator is a child of another element or elements, then you'd need to recursively search for it.
Should be fixed on 2.3.5-pre1