Your KitchenAid mixer jumping when kneading dough is normal as long as the jumping of the KitchenAid mixer is not excessive.
When the KitchenAid mixer is kneading stiff bread dough, the motion of the KitchenAid mixer mumping or bouncing slightly helps relieve the excess torque of the motor.
Although if the bouncing or jumping is excessive or the head also becomes unlocked, you can stabilize the KitchenAid mixer by adjusting the clearance, tightening the hinge or even checking the consistency of the dough.
If your dough hook sits too low, it will push forcefully against the bottom of the bowl and cause your KitchenAid mixer head to jump.
You can use a standard flathead screwdriver to fix it and verify it using the Dime Test.
Place a bowl on your KitchenAid mixer and attach the dough hook.
Then place a dime flat in the bottom of the bowl and turn the KitchenAid mixer to the lowest speed.
The beater then should occasionally brush the dime and move it around an inch per rotation.
Although if it constantly scrapes or does not touch the dime, unplug the KitchenAid mixer and tilt the head back.
Then locate the adjustment screw under the hinge, which is in the neck of the KitchenAid mixer.
Turn the screw right "clockwise" to lower the beater head or left "counterclockwise" to raise it.
And make tiny, 14 turn adjustments at a time.
You can also tighten the hinge and locking mechanism.
As time goes by, the hinge that holds the top half of the KitchenAid mixer can loosen up and lead to aggressive wobbling or jumping.
Start by unplugging the KitchenAid mixer and then carefully turn it on it's side on a padded surface and locate the screw that is located deep inside of the bottom of the KitchenAid mixers neck.
And use a flathead screwdriver to tighten the screw until it's snug to restore tension to the head hinge and also check the silver metal hinge pin that passes through the neck and ensure that it's pushed in and sitting flush on both sides of the mixer.
When kneading dough with your KitchenAid mixer, you should also avoid going above Speed 2, as using a higher speed will overwork the motor and cause severe shaking.
And avoid using overly dry dough as extra stiff dough forces the KitchenAid mixer to work far harder than needed.
You can try adding 1 to 2 tablespoons of water to hydrate the flour more, which can ease the strain on the motor and reduce jumping.
And if the KitchenAid mixer is walking across the counter, instead of the head bouncing, place a non slip silicone mat or even a damp kitchen towel underneath the base for grip.