Sounds like a driver issue/conflict. Did it work originally or has it never worked? If it did, then maybe a recent update broke it and you can try rolling back the driver in device manager. If it never worked, then make sure you're up to date with Windows Updates. Manually check and install anything available. This link doesn't have much more info but it does have a link for manually installing Surface firmware and drivers. May be worth checking out.
https://support.microsoft.com/en-us/help/4023510/surface-troubleshoot-problems-with-windows-hello
Last resort is to open a case with MS, assuming it's still under warranty.