Assertion failed during baking

We are running our bake via command line and keep getting stuck with this error, any ideas?

Assertion failed: FunctionInputs[i].ExpressionInput [File:D:\Build\++UE4+Release-4.12+Compile\Sync\Engine\Source\Runtime\Engine\Private\Materials\MaterialExpressions.cpp] [Line: 7309]

Do you have any fancy materials you have been working on lately? Maybe undoing the last few things you did could uncover a crashing bug.

No, nothing fancy at all. This is actually happening on the basic starter scene that comes default with the engine

Intel Xeon E5-2670 with a Quadro K620

Oh, well that’s weird. What’s your OS version and GPU info?

Hmm, so it’s a starter scene. I suggest baking through the Editor and examining the command-line the editor uses. Perhaps that will shed light on what is going wrong.

I’m not quite sure that I understand what you are suggesting… do you mean opening the editor from the command line, then baking from the editor? Or is there a hidden command line output window that can be access in the editor somewhere that I don’t know about?

I mean, whenever you run a command inside the editor and it calls out to an external command-line process, you can see the actual command it uses in the editor’s output log. For example, that’s the best way to figure out the correct way to package via the command-line.