router bit?

made finger jointer for table router and everything squared up so tried some test cuts 3/8(8mm) on 3/8" ply set bit height 3/8 did test cut. cut first and second gap. the third on clearing pullback chipped layer ply off finger next to cutter. Then last cut it chipped whole finger off.
purchased two sets of four cutters brand new three days ago amazon delivery. Why is it chipping ? made in China.
thanks in advance.