I only know what I have read and watched. The said it was POGO—but perhaps the computer only THOUGHT POGO was occurring, due to bad sensors.
Then—and now—computers only can go by the info they get from their sensors—and if they screw up—often so will the computer. Today—if a sensor reading is WAY out of spec, in such a way not really possible given a normally operating rest of system—a computer will then IGNORE that sensor and inform of it’s failure.
Either way—the other engines burned longer and made up for the lack of thrust, and successfully placed the upper stages into orbit. Nice redundancy. As we all talked about before..this country USED to know how to do BIG things and do them RIGHT. Not too mention back then the “greenisms” did NOT have as much sway on things- as they do today.
Of course—LATER—the REAL malfunction on 13 occurred—to be remembered by everyone—forever. The movie did NOT leave out the POGO problem, or it’s solution (though Apollo 13 movie did NOT say WHY the center engine shut down, it just showed that it did ) and that is a good thing.
An earlier saturn launch, the 4th one I thimk, unmanned—had TWO engines shut down from POGO oscillation.