It’s when the brass is extracted and slaps against the action. Try to remove the sharp edges in the action. Remove the barrel and stick your finger inside the action and feel any sharp edges. Could be a burr or the action was cut so precise and not dehoned it leaves razor sharp edges.
Or what
@spife7980 said. I went through the same issue, had my chamber inspected and honed but the marks still appeared. Found out it was sharp edges in the action. A little dehoning of the sharp edges inside the action and no more cut marks.
Won’t hurt the brass it will develop the cut marks all over the brass the more firings you get.
What action you using?