Seeing it on every knife has me a bit stumped. A lot of knives often aren’t even to begin with… they may look equal but are often offset to one side. You can usually see it by looking down on the tip from the spine side, or at the heel from the edge side. If you’re measuring angles, checking for straightness, etc. this is the only thing I can think of, but I’m not sure it would be that consistent on every knife.
You could double check and make sure the sharpener is assembled correctly… the angle arm is 90 deg. to the base, etc. Haven’t seen a problem in this area before… but if you’re accurately measuring everything, it’s the only other thing that comes to mind.