Try to perform a reset of the Fitbit. Follow
How do restart my tracker
When does my tracker reset and what happens to the previous day data
Your tracker resets your data to zero each night at midnight. For most trackers, your minute-to-minute data will be stored in your tracker for up to seven days without syncing. If you have a Fitbit Alta™ your minute-to-minute data is stored for up to five days. A daily summary of your activity is stored for up to 30 days.
Keep in mind that your calorie burn estimate will begin each night at midnight, so if you're up late and moving around, your tracker will adjust your calorie burn accordingly. Even if you are asleep at midnight, you will still see that you've burned some calories upon waking up in the morning. This is because you still burn calories even if you are sedentary or sleeping. Fitbit calculates your calorie burn based on information about your age, gender, height and weight.