A centre punch makes a small cone-shaped indentation whose purpose is to give the drill point a seat to locate into before it starts cutting.

The rotating drill tip needs to drop into that seat; the depth of the dimple decides whether the tip can settle or simply skate over the surface.

If the indentation is too shallow, it offers almost no seat, so the spinning point slides across the metal before it can bite, which is exactly the slipping described.

Using too much force would tend to make the mark deeper, not shallower, so excess force is not the cause of the slip.

The wrong punch or an over-hardened punch might chip or fail to mark, but a properly placed deep mark of any suitable punch would still have located the drill.

So the fault lies in an indentation that was not deep enough to hold the drill point.

Hence, the answer is The indentation was too shallow.