sacs are much worse than nanners.. they have a full compliment of male anatomy and just 1 sac opening with mature anthers? stamen? whatver... you will have a ton of seeds.
some nanners are nothing to worry about.. 1 seed per oz if bad? lone nanners are soetimes importent or otherwise limited pollen production.
that sac grew a while ago, so keep an eye out... catch'em while green or unopened and all is well. if you can isolate it, that's the better option, but not always possible. like chow said it doesn't gro over night by at day 38, ther's time for 'something' to grow that you'll taste, i bet. and pollination steals resources from bud development too. you got ~3 weeks left if FD 38. the stress was from a while back if there is a fully developed sac 'today' .. could easily be more lurking.