@elexia hold against a source of light, check if it looks any similar to the stopper (can be more pale in colour), check how it behaves after shaking the vial
i can't tell you if it's that or not through the internet, but if it is, the potential harm is relatively low if you're careful
in the future, follow the usual vial coring prevention (thinner gauge needle, sometimes modified puncture angle, focusing the punctures in one spot)