With Visual Studio 2017 (latest rc) - after opening xaml previewer, I am presented with error in the designer 'an exception occurred while rendering the control'. This occurs while trying to view the Android view. I can however view the ios view when my mac build agent is available.
If I click the (!) icon i see a series of exception messages
i.e.
you must call xamarin.forms.init prior to using it
at xamarin.forms.device.get_info()
etc.