Flight Durations Incorrect

Hi,

Sometimes transatlantic flights from Caribbean to UK show up with a duration of <4hrs instead of the correct 7 or 8 hrs. What causes this? e.g

flightaware.com/live/flight/VIR3 … /TBPB/EGKK
flightaware.com/live/flight/VIR8 … /TLPL/EGKK
flightaware.com/live/flight/VIR6 … /MKJS/EGKK

At the bottom of each of the flights you mentioned is this: At least part of this flight occurs outside of FlightAware’s primary service area. Learn more about FlightAware’s coverage