I guess the question is, is that "bulkheadette" really structural?
Can't tell from the pictures but it looks rather small, like the edge of a bookshelf as opposed to a large bulkhead separating compartments.
It sure looks like it let go because of tension from the chainplate above it, but that could also just be fatigue from xx many cycles of tacking, as the tension was applied and released and a marginal bond from the initial layup finally let go.
If there's just a bookshelf there...no big deal. If it is structural, you've probably got to take it apart, slack off the rigging
, fab it back up. Kinda looks like it was finished with that "popcorn" used on home ceilings at that time.