Puff Pastry problems, diagnosed

Do not answer every flat puff pastry by making it colder. During lamination, the butter has to be cool but pliable: if it is too cold it can fracture instead of extending into continuous layers, while butter that is too warm can smear, leak or be absorbed into the dough. After shaping, a different failure can seal the cut layers together: a dull or dragging knife, pressure on the edges, or egg wash running down the sides can stop those edges from opening. A cool oven can also give the steam too little lifting power. The useful clue is what the pastry looked and felt like before and during baking.