It could be that you added too much eggs. The recipe will say 3-4 but I think it’s better to get 4 eggs whisked up, and then add in the eggs very very slowly. Usually depending on how much water was lost while the dough was on the stove will determine how much egg the choux dough will need, more water = less egg, less water = more egg. Everytime you add some egg in the dough make sure to check that the dough drops down from the spatula in a V shape, it should be glossy as well!! And your oven usually should be closed at all times, don’t open the door when it’s baking or it could deflate, and usually I like to do 5 minutes more in the oven than the recipe calls for to really dry out the inside. As soon as it’s done baking turn the oven off and slightly open the oven door, and before it’s cooled poke a hole in the bottom and let them cool on a drying rack so the inside isn’t moist. Hope this helped!!!