Yes, there's a bug that causes timed missions to fail when the captive reaches the door. A lot of people are getting it, and if there is a fix I'd love to know about it.
One of my arcs has the same problem yours does: final mission is timed, failure is supposed to be possible but unlikely, and it has a captive as a required objective. The timer is kind of important, but it had to go, for now.
Eva Destruction AR/Fire/Munitions Blaster
Darkfire Avenger DM/SD/Body Scrapper
Arc ID#161629 Freaks, Geeks, and Men in Black
Arc ID#431270 Until the End of the World
Does making the hostage not be a required objective work? It's an imperfect solution, but for the time being, it will make your arc playable.
Making your captive a non-combat ally set to "wander" or "do nothing" should also bypass the bug, if it works for your story. I haven't actually tested it, but theoretically it should work.
Eva Destruction AR/Fire/Munitions Blaster
Darkfire Avenger DM/SD/Body Scrapper
Arc ID#161629 Freaks, Geeks, and Men in Black
Arc ID#431270 Until the End of the World
I don't know exactly when this started happening but all the negative feedback I've gotten started after i15. Basically, my arc is two missions, last one is timed.
This mission is failing before the timer is up. Only objectives in the mission are, disable bombs (glowies) x4, rescue hostage, defeat boss. I moved it from a 45 min timer to a 60 min timer but still failing. Last test failed with 55 min left on the clock.
This is a lowbie arc with only hellions in it. Anyone else seeing this? I can't figure out how to fix it and I have 33 votes at 4 stars so I don't want to start over if I can help it.
EDIT: I disabled the timer for now so at least I'll stop getting negative voting. But the timer is kinda important for my story.