Hi difalkner, sounds like you are using a re-sharpened bit; at .123" diameter, it isn't inch or metric? Will your control software allow you to input a comp value? As a trial I would suggest making a full width of cut single pass with the bit in question at the depth of cut and feed speed that you normally use and mic the width of cut. If you don't have cutter compensation in your control, you may have to create a new tool to match the cut width that you measured for that particular tool.
I thought initially that this might be an issue of cutter flex, but I believe you've covered that already. I couldn't.t think of anything else that might cause this.