Breakpoints not working when debugging UWP with .Net Standard 2.0

I'm using Visual Studio 2017 version 15.5.5 to create an application using Xamarin Forms that will support iOs, Android and UWP. The shared project is a .Net Standard 2.0 class library.

If I set a breakpoint anywhere in my shared project and try to debug the application using the UWP project, the breakpoint is never hit (if the breakpoint is set in the UWP project then it works as expected). If I start the application using the iOS or Android projects then the breakpoints are hit and execution stops.