DUMPING
Maybe you are able to eat larger quantities of food now which makes you dump. When you ate a couple of bites or one cookie maybe it wasn't enough to do any damage, but now if you eat three cookies it triggers the dumping? Something only you can answer but the only thing I can imagine that would make a difference.
Unfortunately at 15 months I've seen no sign of dumping. I will say though that I really don't eat many carbs, and sugar has been almost non-existant in my food plan.\
Best of luck in figuring this out.