Navigation.PushAsync hangs showing a new page

I have a Master Detail page.
Detail page is created in NavigationPage container.
On detail page I have a button.
On Click I'm doing the follow:

await Detail.Navigation.PushAsync(GetNextPage());

And after this my app hangs.

This does not hang if I remove await.
From documentation it is a bit not clear what exactly await PushAsync means. Will it wait until the pushed page is closed, or until it will initialize and show?