You are past the balance point and holding yourself there with your fingertips. The handstand is not falling, but only because you are paying for it every second.
What it looks like
White knuckles, fingers dug into the floor, and usually a slight pike to compensate. Bails go over the top rather than back down the way you came up.
Why it happens
Kicking up hard puts you past the balance point, and the body would rather be past it: a fall over the top can be caught with the fingers, while a fall backwards cannot be caught at all. So that is where people live, and the fingers pay for it.
What it costs you
Gripping is expensive, and the forearms end the hold before the shoulders would have. It also hides the real skill: you never learn where the middle is while you are leaning on one edge of it.
How to fix it
Come back a touch and let the fingers rest, then balance from the middle of the hand with short presses rather than a constant grip. Fingertip balance work at the wall teaches the range, and a softer kick-up stops you arriving past the point.
Drills that fix it
Fingertip balance drill
5 × 20s of deliberate small drifts.
In a hold, deliberately let yourself drift forward and stop it by pressing the fingertips. Then drift back and stop it with the heel of the hand.
How Nstand measures it
Nstand measures where your mass sat relative to your hands, in torso lengths and in the direction your chest points. More than 0.15 torsos ahead of the hands, averaged over the hold, is called weight over the fingers.
It is a camera and some geometry. It does not replace a coach, a gym or an academy, it cannot see your wrists, your history or what you are about to land on, and it is wrong sometimes. Handstands can injure you. What you do on your hands is your decision and your risk: warm up, train where a fall is safe, and stop when something hurts.