I’m going to answer in English because my Deutsche is so horribly rusty.
Those lines look like the issue discussed in this thread. What was happening in that case is that the model was composed of separate shells which just barely touched. In this case, is the back of the extruded letters coplanar with the front of the base? If so, it is probably this issue.
What is happening in this case is that when PreForm slices through the plane that’s shared by the two objects, the math gets rather degenerate and there’s a lot of confusion about what portion of that slice is inside and what portion is outside. There are two ways to make this more robust.
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If your modeling program supports it, you can do a “boolean union” to combine the separate shells into a single one. This is the preferred approach.
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If not, then you can push the back of the letters a tiny ways into the base. Something on the order of the layer size you’re going to print at will be more than sufficient. The math of two shells which intersect is much simpler than the math of two shells which just barely touch.
I hope that helps.