Latest Xamarin update rolled out during the weekend (15.2.2 - Weekly Virtual Machine / Stack updates - 2017.05.27)
If you’d still have the MTOUCH: error MT2001: Could not link assemblies issue the recommended solution is to upgrade the Xamarin.Forms package to the latest version (2.3.4.247).
Related Xamarin issue tracker link: https://bugzilla.xamarin.com/show_bug.cgi?id=56296