First, make sure that the flights in question are from the past (we only document past flights).
Try going to the "Trips" screen (the list of your past and future flights) and clicking "Pull to Update". This should update both your sync status and statistics. Restart the app, and the check will start again.
In most cases, the flights will be placed in the "People" or "Other" folders. Only flights in "My bookmark" are counted in your statistics. Read more about transferring flights between bookmarks here.
If these recommendations didn't help, please contact our support team via the feedback option in the app settings.