It's an incomplete coin which has not fallen into the scrap bin when it passed on the vibrating sieve.
The blade comes and passes through the equipment punching blanks. Thereafter, the blanks pass through a vibrating screen to keep only the good ones. Sometimes, for several reasons (slip of the blade on the conveyor, misalignment of the blade with the guides on each side, etc.) can produce a clipped coin.
Blakesley effect, from the name of the american who saw it first, is almost always visible at 180 degrees on the opposite side of the cut.