This happened to me too.
It was because there was one enemy left before I jumped off the Titan.
Reload and make sure you've killed them all.
I can't get off the attack boat and I obliterated everything on the Titan with the 20mm. I even shot everything up after the enemy shots stopped. Floated around the Titan slowly for 15 minutes hoping to see something or draw out any stragglers, but nothing. I'm gonna have to start that level all over again I guess.
I did it. The problem was falling off the Titan when it split. You need to stay on it until it's time to jump off after killing the enemies.
