you probably didnt declare your InverseBoolConverter or you have some problem on your xaml. click continue and read your output window to see the actual error.
your question is not clear but as much as I can understand, yes always use ObservableCollection. Mvvm is better approach with Binding instead of directly assigning ItemsSource property.
you can download your data using api, wcf or any other webservice approach or you can embed your data in sqlite into the project if your db is small and you dont want to amend it frequently. Akavache is good library for downloading from cloud database.
@christophedm but you are getting also app.xaml.cs 31 information which tells you where the error occurs. it is still useful in my opinion. In general, Hockeyapp, Xamarin insight. they all do same thing. not sure about mobile center, i havent tried yet. firebase looks promising but I need a solution for UWP as well.
https://github.com/luberda-molinet/FFImageLoading supports animated gifs also. I am using in my app and works perfectly fine
enable multi dex on android options will fix it also