Fuel data analysis requires a deeper look if false refills/drains are suspected.
The main reasons for incorrect records of fuel drains and/or fill-ups:
Tracking device has power supply or ignition issues;
Vehicle operates or drives on an uneven surface causing fuel splashing in the tank;
The vehicle is tilted;
Vehicle is being transported on a trailer;
Malfunctioning fuel sensor in a two-tank fuel system;
Fuel flow while the ignition is off in a two-tank fuel system with CAN-bus data;
Non-standard shape of the fuel tank on special vehicles.
More useful information on drains can be found here.