Souls. Scientists have stumbled on a method of converting base matter into immortal souls. Unnoticed on the floor of the lab, their creation eventually slithered off to inhabit a politician who had sold own soul in a futile attempt to regain national prominence. The devil is mighty pissed.
On the other hand, it may just be that the mass measurements weren’t as good as the researchers thought. Or that the journalist who did the story reported on things before that were not ready for publication. That sort of thing has happened many times before.