First, make sure the flights in question are in 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 refresh". This should update both the Sync status and the statistics. Restart the app and then the check starts again.
In most of the cases, flights will be placed in the People or Other folders. Only flights in "My bookmark" count toward your stats. See more here about transferring flights between tabs.
If these suggestions don't help, please contact our Support Team via the feedback option in the app's settings.