This what I got from the ingredients:
"potato starch , rice flour , modified maize starch , buckwheat flour ,vegetable margarine [vegetable oils and fats in varying proportions (high oleic sunflower oil, shea butter), water, salt, lemon juice, emulsifier: mono-and diglycerides of fatty acids]. , yeast , glucose-fructose syrup , sugar , salt , thickener: hydroxypropyl methylcellulose ; emulsifier: mono- and diacetyl tartaric acid esters of mono- and diglycerides of fatty acids ; raising agents: ammonium hydrogen carbonate ; natural flavouring . "
Basically, any of those ingredients could cause upset if you are sensitive to them. The only ones I could see that would be more unlikely to were : sugar, salt, and water!! I am not scientific enough to know if the " diacetyl tartaric acid esters of mono- and diglycerides of fatty acids "are okay or not.....etc.
If you can usually eat rice, then rice flour might not have been the culprit. But don't assume if you can eat potatoes, that "potato starch" is the same, or if you can eat corn, that "modified maize starch" is okay.
I am sorry that happened. It's hard to find gluten-free stuff that tastes anywhere decent, and now you are in a jungle of "what ingredients might upset me?"
I do empathise, as I have had endless hours trying to find quite pure products of processed foods online, and usually come up against a fat brick wall, or an immensely high cost.
It may be very inconvenient, but if you can figure out which flours and fats you are okay with, you may have to obtain those from a health food store and make your own breads, crackers, breadsticks etc.