Don't over stuff the ravioli.
1) as you seal them, the filling seats out of the edges, creating a bad seal and ultimately falling apart when boiling.
2) The more filling you put it, the more the ravioli expands as you seal it up. This stretches the dough, making it , sometimes, too thin. This also can make them fall apart when boiling.
Luckily, this time around, I was smart enough to have learned from my mistakes made int he past, so I had no casualties.