If you use FitBit tracker with a smartphone which has been recently undated to Android 5.0 Lollipop, you might faced the same problem as me - the Fitbit app has stopped synching with the tracker.
Surprisingly there are a lot of people complaining online or even raging in putting one star rating to the app in Google Play. However, the solution which helped me: uninstall and reinstall the app, is mentioned on the FitBit Help web-site, and it takes around a minute to remove and reinstall the app.
It seems I need to repeat deinstall/reinstall procedure each time the phone goes into power saving mode.
Recently, Fitbit has released sevaral new versions of its app and it looks like they have fixed the problem as I no longer have any issue with synchronisation. Well done Fitbit!