Is the mech 4th job test broken?

Is the mech 4th job test broken? I've killed the boss behind the 4th job instructor 3 times but it still says I haven't killed the boss for the 4th job test in the quest helper. Is there another boss that uses that room for some quest I activated but never completed? Does it fail if you kill it too fast? (It doesn't take very long to kill.)

Thanks for any help!

If you are in a party it can bug up and fail to count the kill for the quest.