I'm trying to fix linker errors by ensuring I'm referencing the same version of GooglePlayServices as SimpleAuth. In doing so, I noticed that Sample.Droid is still referencing 42.1021.1, while SimpleAuth now references 60.1142.1:

SimpleAuth.Google.Droid.csproj:

<PackageReference Include="Xamarin.GooglePlayServices.Auth">
 <Version>60.1142.1</Version>
</PackageReference>

Sample.Droid.csproj:

<PackageReference Include="Xamarin.GooglePlayServices.Auth" Version="42.1021.1" />