If you use Luban, do you see this in Luban gcode preview too? What else slicing software do you use if not Luban?
If it’s there, please roll back one or two Luban Versions and compare the preview.
You should even be able to use another gcode preview software or online preview but maybe you have to change the .nc extension to .gcode.
Admittedly, the close-up makes me think if it is material related or code related… In that test you’re burning so deep the top layer is obviously gone… Still, to be sure, I’d recommend to try another wood brand. Also, what others suggested: Load the code into some GCode-Previewer and check if you can spot the pattern there.