Ability of any electronic flash to take multiple shots in rapid
succession is generally associated with the design of the flash.  Those
that can do it basically 'ration out' their power so that the
capacitor, which stores the electrical energy that goes to the
flashtube, is only fractionally depleted with each shot in the series.
Example, each shot consumes 1/5 of total power on the flash unit's
capacitor, resulting in ability to shoot 5 shots in rapid sequence.
You SB24 was designed for rapid sequence, your in-camera unit was not.
Makes sense, since the flash has more room internally for larger
components, including a bigger capacitor that the one inside your
camera!