I, along with many people, have trouble with the Fitbit app. The steps disappear soon after syncing, and no amount of troubleshooting is helping. This is very frustrating because the Fitbit app usually has great information, but it's all gone. I've found another app that I use, Optimity, has Fitbit integration, and that app shows all steps one week at a time, even when the Fitbit app has nothing. I just wish it showed the month. The Optimity app is used by the ParticipACTION program. Other app that link to Fitbit might also be handy.
