Possible explanations and actions:
1. Incorrect settings for trip detector.
The option to analyze fuel filling only at stops is set on the 'Fuel Consumption' tab of unit properties, however, the Trip Detection is not adjusted correctly. Either disable filling detection at stops or change trip detector settings (in particular, increase minimum moving speed or maximum distance between messages).
2. High filtration level of FLS.
Decrease filtration level of FLS on the Fuel Consumption tab (recommended are values up to 15) or set the option 'Calculate filling volume by raw data'.
3. High value of minimum filling.
Decrease the value of minimum filling volume on the 'Fuel Consumption' tab.