With a bit more fiddling around I get this [error] precondition failure: invalid attribute id: 2189977 AttributeGraph precondition failure: invalid attribute id: 2189977. And finding similar errors elsewhere I remembered that I changed a NavigationView to a HSplitView (?) which seems to behave the same . After reverting to NavigationView this crash goes away ! Is this a bug? and should I raise a bug with Apple for this ?