In Nature and in a published preprint, Illinois professor Prashant Jain has explained "an important confounding effect" that helps unravel the mystery surrounding recent reports that LK-99, a compound of copper, lead, phosphorus and oxygen, was working like a superconductor at room temperature and ambient pressure.

The LK-99 mystery began in late July when a start-up firm in Seoul published claims that LK-99 is a superconductor at normal pressure and room temperature. The news quickly spread worldwide, because all known superconductors function only at very low temperatures and extreme pressures.

The Nature article says that "after dozens of replication efforts, many specialists are confidently saying that the evidence shows LK-99 is not a room-temperature superconductor," and Jain explains how impure samples of LK-99 could have led to an important confounding effect.

More coverage here: 

The room-temperature superconductor that wasn’t | Ars Technica