First, confirm whether the Breathing score is enabled in the APP. The path to enable it is [Mi Home/Xiaomi Home] APP >> [Device] >> [Sleep] >> [Breathing score]. If the sleep duration is too short, the effective monitoring duration will be insufficient to display the sleep data(Nighttime sleep duration should be more than 3 hours.). An improper wearing method will lead to the inability to monitor the Breathing score. It is recommended to wear the device not too loosely, and the device should be one finger-width away from the wrist bone.
If none of the above reasons apply, verify whether the APP and firmware versions are the latest. It is recommended to restart the band or unbind and rebind the band to try again.