Not very many people go to UC Davis, unless they live around there or have a CMS. Sorry you can't get feedback from people with actual experience.
What happens when anyone has GI issues, whether it's vomiting or diarrhea, is that you lose fluid AND electrolytes. Any imbalance in things like magnesium, potassium and calcium will have an adverse effect on MG or CMS. Did they do a metabolic panel on your son? It's a simple blood test that is often standard for someone with MG who is doing worse. If you don't know what's wrong, how can you fix it?

And you can't assume a deficiency of an electrolyte and throw a banana (potassium), chocolate (magnesium) and milk (calcium/magnesium) at it.
I hope the appt. goes well.
Annie