This is a new one. And I’m sure it wasn’t happening earlier this morning, using basically the same carving parameters. It started after I went back to Onshape and adjusted some dimensions slightly, which required starting over with a new part in KM. (I’ve been running D12 all morning.)
I’m experimenting with using just roughing and outlining to do a waterline contour of my part (so that carving marks are better aligned with the shape of the part). So I have the outlining step-down set very small: .005".
I think the problem is pretty clear from the preview and animation results. The low altitude moves that cross through the part happen after the outlining gets below tab height. They’re the rapids that happen between the “troughs” formed between the tabs.
I’ll email you an export of my workspace/profile.