Like Subject say, i noticed a strange behavior of the 3D Surface Op, using the Patern option ZigZag.
If i work with an Step Over of 100 or 50 i get the expected path.
If i change the Step over to something else, the path looks like this:
The amount of the jumps differs, depending the value of the Step Over.
If i select the flat area above of the "bumps" to, i get a path without any jump, no matter of the value for the Step Over.
If i deselect Boundary Enforcement, i get also a Path without jumps (but the path dosn't fit to my router then...).
OS: openSUSE Tumbleweed (KDE//usr/share/xsessions/plasma5)
Word size of FreeCAD: 64-bit
Version: 0.20.24612 (Git) AppImage
Build type: Release
Python version: 3.9.2
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.1
Locale: German/Germany (de_DE)
The File is to big to attach it, if someone wants to have it, i'l make smaller example (which hopefully shows the same behavior... )