Not sure if it's helpful, but I generally suffer from IBS (or just a super sensitive GI tract?) and MANY things (supps, foods, drinks...even just certain situations!?) can cause problems for me (awesome eh?)....but I don't think Ultima has ever caused me any problems. At the same time, everyone is different and if it DOES turn out to be Ultima, maybe you're just a bit more sensitive to something in it than the rest of us? The only downside with Ultima is that it has so many ingredients, it may be tough to figure out exactly what in there is causing you problems.
Good luck!