In order for Track Log to record automatically, make sure you have checked the following:
1. Ensure that you have a GPS source connected. If you have a WiFi-only iPad, you will need an external GPS receiver.
2. Open ForeFlight and go to MORE > SETTINGS > TRACK LOG and make sure the switch is ON next to ENABLE AUTO START/STOP.
3. Make sure ForeFlight Mobile is open and running on your device and showing (in the foreground).
4. Make sure the iPad is not asleep. Of note, once a recording is started, the app can be backgrounded and/or the iPad can be allowed to sleep as long as you are using the internal GPS receiver or a Bluetooth external receiver.