EIDOS Montreal and Nixxes have released a new PC update for Shadow of the Tomb Raider. According to the release notes, PC patch #9 brings various fixes towards audio issues, ANSEL stability and Co-Op Mode stability, and adds Friends leaderboards to the Challenge Tombs menu section for each Challenge Tomb & Mode.
Source: N4G PC Shadow of the Tomb Raider December 18th PC update fixes audio issues, Ansel & Co-Op Mode