Hit the broken door 3 times and it still didn't flag. Then I get charged by a Zerg. I sacrificed myself to flag that keep and what do I get in return. A big waste of a ballista.
if your using fire siege it has a chance of not lighting said keep, you can repair through fire aswell. Been a long known bug thats just been accepted as the new way it works, killing guards usually has a better chance of lighting it. You gotta use stone trebs and (for DC) covenant ballistas