The sample code from the Collection Fixtures section of the documentation doesn't even work for me with NCrunch. Copy pasting that code, and adding a useless Fact was the first thing I tried to make sure that it was failing in my main problem wasn't a syntax error on my part somewhere.
I can copy paste that example code here if you really need it, but I only added a function with Assert.Equal(1,1) in it.
It's not something I have ever changed, and it is indeed set to UseDynamicAnalysis. Now that I am aware of the option, changing it to UseStaticAnalysis actually seems to make NCrunch unable to see any of the tests, and it reports that it is monitoring no tests.
For xUnit, I am using the 2.0.0 version off NuGet. However, I have tried 2.1.0-beta and get the same issue.