Visible steps when engraving (but only sometimes)

This sound ominously familiar:

There is no resolution yet, but if you work through the same tests and also find nothing wrong, that’s a useful data point.

How big are those pieces you’re engraving? That will give us some idea of the overall scale: are the ripples 0.1 mm or 1 mm long?

Do the “good” and “bad” results differ in alignment with respect to the axes?