You mention sacks - MALE plants????????????????
Female plants can pop male anatomy when stressed. In this case it looks like an overfeed of Nitrogen during flower.
If the sacs are not producing pollen, and they fall off easily I wouldn't worry too much. I've had quite a few sacs on smaller branches that haven't produced much pollen, if not any. But if you want to be sure you can remove them or the effected area. It's the plants natural reaction to conditions out of its comfort zone. The female plant will sense oncoming demise or loss of health and make a last ditch effort to reproduce.
A seed or three isn't really an issue with stressing over too much. If there's a few there, there's probably more to be found.
Heat, light, environment, pH variance or nutritional shock can induce stress rodelization, and some plants have genetic hermaphroditism in their "blood" line.