Many things, start with checking that the acorn nuts at the top of the daggerboard plate are super tight.
Check that the daggerboard plate is tightly attached, are there acorns on all bolts? Look under the plate.
Locktite is your friend.
Are the recessed holes in the bottom plate that the top plate nuts sit into tight? Is it snug?
When the boat is out of the water on a crane with the daggerboard/keel bulb down, grab the keel bulb and see if it rocks back and forth. If so you will need to tighten the bolts holding the keelbulb onto the daggerboard. The nuts are recessed in the keelbulb. They are bonded into place, so you will need to dig out the bonding material so that you can gain access to the nuts. Then tighten the nuts with a big torque wrench with as much strength as you can muster. Locktight is your friend. Then seal the nuts into the keelbulb again.