I don't even know why ME2 has such a stupid mission in the first place... Boring, overstays its welcome, and the reward is laughable.
Anyway, I did it yesterday, Xbox as well, had the bug as well... But it did not affect completion.
You sure you had all power cells? There are four, not three.
1) Immediately at the starting area
2) After the mech breaks the first wall, there's a fissure in the ground, cell is on the far side of it
3) At the varren spawnpoint with the flaming pipe
4) Right at the final turn on the right
If you did, then it's a bummer.
