When cutting a profile with an 1/8" end mills (either straight or spiral) I get these lines which coincide with each pass. I have tried reducing the plunge rate (use 30in/min now) and run the cut at between 20 and 40 in/min. Still get them all the time.
An out of true bit, for any reason, can cause minute vibrations which add to bit deflection and tear out, and more so with different wood types, speed and feed settings. Some woods are more prone to this as Phil posted. For the OP it may be a combination of issues.
An unsharp bit (even ever so slightly) will at the very edge compress the wood fibres and fail to cut these fibres completely, the CNC complete the pass, dig into next level and carves again. Now the last cut edge is cleared but the partial cut fibres will be torn off instead of cut off. So what you are left with is a frayed edge/step.
Sharpening of the tool may help. Harder wood also, dryer wood vs wet wood will make a difference. There are many factors at play.
Visually the “defect” is pronounced but dimensionally it may be spot on.