I created a Simbrief flightplan for the MSFS B747-8i from KOAK to KLAX.
Simbrief gave me a fuel quantity for that 1 hour flight of 15,000 Lbs. (less than 1% of the fuel tanks capacity).
As a result the aircraft ran out of fuel and crashed.
I have found that the fuel quantity should be at least 50,000 Lbs.to give a comfortable margin. (That is some 12% of the fuel tanks capacity.
I hope Simbrief can fix this bug.