Hi, thanks for sharing this problem.
This problem is in NCrunch's integration with the .NET Core platform. It's a limitation caused by the side-by-side versioning of NCrunch's .NET Core libraries (which are on .NET Core 1.0/1.1) with the .NET Core 2.0 environment.
We've been looking at ways to resolve this, but as the most feasible way seems to be to remove support for .NET Core 1.1 test projects, it's something that may happen much later down the line.
To fix it, just introduce a Nuget reference from your test project to System.ComponentModel.TypeConverter.