Not really an answer but thoughts for further investigation:
IF the code is not in a loaded module, it’s likely on-the-fly generated code. That type of things can be done for many different reasons, though COMToCLRDispatchHelper would suggest the layer converting the historical COM interface to a CLR component needs some generated code for marshalling the parameters from one world to the other.
You can investigate that bit further by introspecting the heap itself, and try to find more information about the allocation that contains the code.
That said, I don’t think that’s likely to be your culprit. I would rather think the problem is in the one call you didn’t find symbols for (mscorlib.ni.dll), which means investigating that is going to be hard.
Without symbols, you’re probably stuck with debugging its dissassembly and try to understand what it does by inspection.