In my experience, the MonoDroid debugger often breaks down - and PCL support is obviously also โnascentโ at best.
Developers can help you with tips such as "make sure you have a quick deployment and a general (debugging) SDK," but basically you need to ask Xamarin to fix it.
My advice is to register and troubleshoot Xamarin through their forums, through bugzilla and through any customer support contract you have.
In the meantime, without the MonoDroid debugger, it goes back to WinRT and WP (and MonoTouch on Mac) to debug your PCLs - or go back to the "old skool" methods, for example add tracing
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