You most likely short stroked it.
My recommendation- visually inspect each and every charge as it is dropped and then immediately place the bullet. For .38 this might mean removing the case from the press. In this case, place the bullet before returning the cartridge to the press (to avoid the chance of double charging). Also, when you spot check a charge, get in the habit of visually inspecting that you are returning an empty case to the press and then again, inspect the new charge that you throw.
Follow those steps every time and you will be squib free and double charge free. Pretty soon it will become a habit. At this point the thought of placing a bullet on a case that I havent just visually inspected would seen foreign to me.