Why is some or all of a recent drive or charge missing?

There can be a number of reasons why a period of data may be missed, but the most common are:

• The vehicle was offline or unreachable. This can happen if the cellular connectivity in the vehicle drops, it is out of a cellular coverage area, or if the vehicle fails to re-connect to cellular after waking up. This usually resolves on its own, but you can also force the vehicle to reset connectivity by holding down the steering wheel buttons and pressing down on the brake until you see the Tesla logo on your screen. Your car should then reconnect to cellular.
• Tesla's API was unavailable for a period of time (this is fairly rare, but does happen from time to time).
• Your Tesla Account authorization expired and you haven't had a chance to re-authorize it.
• TezLab was trying to let your vehicle sleep when the drive/charge started, by default, this starts 1 hour after the last movement of the vehicle. Try adjusting your sleep settings or open the app to force data capture. (Please see Sleep Modes for more.) 
• TezLab is trying to let the vehicle sleep but another third-party app is keeping it awake. (See Multiple Third Party Apps and Sleep) This can lead to longer periods of non-communication while TezLab waits for your vehicle to fall asleep. Try adjusting your sleep settings as much as possible so that they line up between apps.