I don't know if that really addresses the problem but I will try it.
The issue seems to be why does cura happily print one thin wall (the one which is orthogonal to the printer axes) as repeated single lines, but prints the other thin walls as (short segs one slice / single line the next slice) ? I can't see why it doesn't just print repeated single lines for all the slices ...
That seems strange behaviour ...
There are rounding errors both in freecad and in cura. You need to either make those walls 0.41mm or change your line width in cura to slightly smaller (by about 0.01mm).
A 0.4mm nozzle prints reasonably well from 0.33mm to 0.48mm - really it can print beyond that - for example from 0.3mm to 0.6
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