On a threadless headset, the star nut and the bolt that goes into it through your top cap
do not actually hold your bearing adjustment. you need to loosen the machine screws that
tighten the sten onto the fork tube, then reset the bearing preload using the top cap bolt,
then retighten the stem in its new position.

It's also possible to damage or lose a spacer. They need to go up a little farther than the
end of the steerer tube in order to set that preload.