If the fuel shutoff valves are closed that's an instant flameout. They should never be operated unlesss required by an emergency checklist.

In the real 727 you would never run into a situation where the #1 & #3 boost pumps were on and the tanks were empty (hopefully).

Maybe the CS simulation is setup that fuel will not crossfeed from tank #2 to engines #1 & #3 with the boost pumps on. It could be a software issue, But the 727 should never be operated in that configuration.