If you find that some drives are missing then make sure you have the following enabled and checked.
1. Minimum drive duration by default is 3 mins. This means any drives less than 3 mins will not be tracked. You can lower or increase this value inside your app under your Profile Settings (furthest icon from the footer nav) as pictured.
2. Enable highest accuracy mode. This mode will improve tracking accuracy, but will also increase battery consumption.
3. Make sure your battery has sufficient charge or is plugged into your car's power adapter. iOS drops GPS updates when it goes into low power mode.