The point is that vertical lines appear with the same frequency as the halftoning matrix. What causes the problem is the way to cycle the layers along Z. That is, each of the layers is fine, in the XY planes there are no patterns. But the way the halftoning layers (or ht for short) are painted on top of each other isn't very elaborate. The matrix is translated in the XY plane a fraction of its size. This ensured that each layer was different from the previous and following ones and did not repeat until a certain number of layers. There is a parameter 𝑛 in the system that refers precisely to that. For a value 𝑛, the offset in XY is 𝑠/𝑛 where 𝑠 is the size of the halftoning matrix. Usually, the bigger value of 𝑛 the better. But once 𝑛 reaches the value of the square root of the size of the matrix, continuing to increase its value becomes counterproductive, since the pattern of the next harmonic begins to be favored.
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INC, HP, "TONE-CYCLED HALFTONING FOR Z AXIS PATTERN UNIFORMITY IN 3D MJF", Technical Disclosure Commons, (November 21, 2022)