I’ve never bothered with breeding ball pythons, and haven’t encountered these with boas. Now with that said I’ve heard they’re not actually sperm plugs, but cloacal castings. More or less a shed from within the cloaca.
@randall_turner_jr is right the old school term is sperm plugs but they are not, as @randall_turner_jr stated. This being a female it really couldn’t be casings either. The new science for females is they don’t have scent glands (the little white things we see when we pop them) but actually hemiclitores. That looks almost like that in the pic, but I don’t think they can shed off. I may be wrong, but like you I have never seen that in over 20+ years myself. If you have looked over the snake, and she is not missing scales or anything wrong with her cloaca - I would suggest it is just some weird piece of twisted up shed or some sort of fecal matter? I hope it is not anything parasitic. Very strange, I would quarantine and see if anything similar happens next time she sheds and poops. Hopefully someone will see this and know exactly what it is, very weird! Please keep us updated, I want to know what that is!