The problem comes from small segments.
This is the problem with RoundCorner, as it is based on a pure geometrical approach. It may also an obscure bug. The zigzag artefacts disappear with an offset under 2mm.
So there is no good solution except may be
to scale up, as suggested by mitcorb
to put the option "Strict respect of offset" ON
but beforehands to try to eliminate the few small segments by adjusting the upper surface.
RDC Bug WorldWiz.png