Sync to your fitness tracker fails constantly, and you end up having to constantly enable and disable the sync, with the occasional app re-install to get it to work. This is painful enough, but as there can be rewards based on step count over a month it is infuriating to find you've missed out yet again because of software failure. You can get it to remind you to check sync when you configure it, but when you have to do it again it will stack the reminders so you get them all day.