Here are the ingredients. I’d suspect either you’re reacting to the inverted cane sugar (as opposed to the normal type) or the cause is hiding in the “natural and artificial flavors” industrial secrets catch-all.
Inverted sugar is simple sugars combined physically, but not chemically (in which case it would just be regular table sugar, sucrose). Inverted sugar has a different flavor profile than sucrose. It COULD be the problem. I can’t say for sure, though. Who knows what that “natural and artificial flavors” has in it?