Xamarin.Android warning XA0107
Issue
The Xamarin.Android build will emit a XA0107 warning if it is using a "Reference Assembly" during the build, where it shouldn't be. These are sanity checks that likely mean there is a bug in Xamarin.Android.
XA0107 means that a file such as System.dll located within the Xamarin.Android installation is being passed as input to one of the following MSBuild tasks:
<BuildApk />
<ResolveAssemblies />
Solution
Consider submitting a bug if you are getting this warning under normal circumstances.