There could be any of these two reasons. 1. The dough is soft. After frying it looks crispy, not flaky. But as soon as samosa cools down, the crust becomes soft and soggy. To avoid that, always knead the dough to medium stiffness. 2. The oil temperature is low. If you have added samosa into not hot enough oil then it will soak up too much oil and result in a soggy samosa crust.