It might well be that the log is sliding slightly as you cut as others are suggesting. I can't say I've seen this with my wire cutter, but I have seen it when cutting with a bench scraper blade. If this is the case, the cutoff bar should be narrower at the bottom than at the top, because the heaviest part of the log will want to slide away from the cutter.
Another possibility is that you inadvertently misaligned the blocks on either side of the cutter arm when you adjusted the tightness of the bolt and nut. Those blocks need to be perfectly vertical so they keep the arm perfectly vertical. If they are not, the arm will make a correct perpendicular cut when looking at the top of the soap log, but the cut will not be vertical when viewed along the side of the cut, just like what is showing in your pics.