When you're making pasta, whether you're using gf flour or conventional flour, and the dough forms but breaks, it could be for a few different reasons. The most likely is that you haven't conditioned your dough enough. Pasta dough needs to be kneaded, rolled, and folded multiple times before it's ready to be rolled thin and cut. It can also happen if the dough isn't hydrated enough. Perhaps the eggs you used were a little smaller than normal, for example (hence I recommend weighing the eggs out of their shells).