Roslyn semantic model GetTypeInfo on method invoke argument is null

Question

I'm trying to analyze something like blah.SomeMethod(x => x.PropertyA) in a method call and get the class of 'x' and property referenced so I can go verify that property has an expected attribute attached. I want to analyze the first argument to the method call.

So I make a Roslyn visitor and give it a compilation/SemanticModel from the VS Project (in an existing solution) and find the method invocations like so:

var workspace = MSBuildWorkspace.Create();
workspace.LoadMetadataForReferencedProjects = true;
var solution = await workspace.OpenSolutionAsync(pathToSolution);
var project1 = solution.Projects.FirstOrDefault(proj => proj.Name == projectName);
var document1 = project1.Documents.Single(d => d.Name == documentFilename);
var tree = await document1.GetSyntaxTreeAsync();
var compilation = project1.GetCompilationAsync().Result;
Debug.Assert(compilation.ContainsSyntaxTree(tree));
var semanticModel = compilation.GetSemanticModel(tree);

public override void VisitInvocationExpression(InvocationExpressionSyntax node)
{
    string methodName = node.Expression.ToString();

    if (methodName.Contains("SomeMethod"))
    {
        // Analyze each parameter in the method call
        foreach (ArgumentSyntax argument in node.ArgumentList.Arguments)
        {
            // FIRST ARGUMENT HERE IS x => x.PropertyA.  I want to get the 
            // class and property names.

            // The below returns an object with properties: 
            //   CandidateReason: None
            //   CandidateSymbols: Length = 0
            //   Symbol: null
            //   Type: null
            var typeinfo = semanticModel.GetTypeInfo(argument.Expression);

            // node type info is empty, too, and its parent.
            var nodeTypeinfo = semanticModel.GetTypeInfo(node.Expression);
            var nodeParentTypeinfo = semanticModel.GetTypeInfo(node.Parent);

            ITypeSymbol parameterType = typeinfo.Type;
            if (parameterType = null)
            {
                // Always null, doesn't break.
                Debugger.Break();
            }
            //...
    }
}

As you see, the GetTypeInfo() always return None/NULL on the argument, the method (node), and the node's parent.

Even GetSymbolInfo() on all the above returns None/null as well.

I know the types are compiled as part of the project, so why can't Roslyn find anything? It's like the semantic model (from the project's compilation) contains nothing.

All I can imagine is that since some of the classes used are in a different project which is referenced by the project I'm compiling, the semantic model of the main project won't work at all?