Thanks, yes, there was a stroke, but it was disabled in the Appearance tab, that doesn't make a difference, does it?
I just found a workaround myself, although it's a little more complicated, it still achieves the same thing:
I duplicated the black element, made it white and put it under the other two elements. Then I moved the white spikes above the original black body and performed a Alt+Subtract action on both (black body + spikes)
. This is the new setup, it doesn't cause any ghost lines to appear.
Here the new exported image:
(The new file is attached)
I still think, this bug should be fixed, since my original approach should, following the logic of Designer, work and is much easier to achieve
solution.afdesign