i had same issue today. I woke up and steps, calories etc were not set back to 0 at midnight. So i have in the morning already 123% of my goals achieved. I made a factory reset of the band and now the band itself is showing 0 but it is definetly a bug as i have it already for a week and never did this before
however it tracked down my sleep correctly.
as workaround after factory reset all the values are set back to 0 in the health dasboard so at least i don't have 120% of the goals completed