My opinion might be the odd one out, but I think your soap might be too hard. So you really can't go through soap in one smooth motion leaving those marks. It looks like your cutter or knife stopped and then start cutting again. I hope you know what I mean, it's like when you are cutting hard block of cheese.
I am using big knife and this happens if I use it on soap that harden too much.
Now I usually cut the morning after, so when soap is around 16h old and get really smooth bars.