If you’re engraving a picture/photo using passthrough, you will get a “blank line” at the point where the steps break. It’s not an alignment issue, I’ve done multiple passthrough engraves and the alignment was absolutely perfect. As best as I can tell, it’s the way they convert the image from (whatever format) to (what is needed for the laser) - the edges are not continuous, the compression/conversion/whatever assumes the space beyond the edge is “white” so the first line or two are not as “solid” or dark as they should be. They break the image into sections and process individually, instead of pausing/splitting the engrave in “laser speak”.
Put another, simpler way - the first pass of the laser on the next step does not fire, or fires at a much reduced power. I’ve visibly watched this multiple times now. I’ve had to touch up passthrough engraves with a pencil.