Built the SDKBrowser project for iOS, using VS 2017 and latest stable Xamarin.Forms.
When editing a field, the OS keyboard appears and above it are "Prev" and "Next" buttons for moving between form fields.  Those buttons behave erratically.  Attached 2 images.

01: the 1st field is focused.
02: after pressing Next, the 3rd field is focused ("Age").

Pressing Next again does not change which field is focused, and Prev becomes active.  Pushing either Prev or Next does nothing at all.