Quest Failed? How?

[No' Name]

So, I'm on the last boss of the story, everyone is alive, nothing is going off, and the boss is down to 25% HP.

Suddenly, it pops up, saying I've "failed" the quest?

Um.... What...? Everyone is Alive....

I've had this happen to me a few times, same exact scenario, everyone is alive and doing well, boss is near death, they're not casting an insta wipe skill or anything. Is this some kind of a bug? It really feels like a bug to me. All that happened afterwards, was the game saying try to do some quests to lvl up and get stronger.... I'm lvl 55 across the board.... What.....?

[Linfried]

All characters share the same Critical bar and that bar does not reset until the next boss fight.

[Decoy]

I looked into the "Critical bar" mentioned above and found this:

The critical gauge constantly depletes as long as any character is in critical condition.
When the critical gauge reaches 0 during a main story battle, you'll get a game over.
When the critical gauge reaches 0 during a quest, you'll fail the quest.

[Nepnep]

Maybe you failed to save a certain someone?