Too much filling would definitely cause your empanada to burst open. First, it will be more difficult to fill the empanada. Second, as the filling heats up, it produces steam, which fights against the seal you made. With too much filling, you'll get a lot of steam and a tenuous seal.

Why are my empanadas opening?

The main ingredients are water and corn flour. If you don't work quickly, the dough will dry out and start to crack. Cracked empanada dough means that your empanadas will also have cracks in them, which means oil seeping into your filling in the fryer and drying out your empanada. Or, worse, causing an explosion.

Why are my empanadas bubbling?

The crust forms while some of these little pockets of trapped steam are at fully inflated just below the surface. Thus, the even after the dough cools and the high pressure of the steam inside the bubbles goes back to normal atmospheric pressure, the crust is rigid enough that the bubbles keep their shape.