the nozzle that is used gives the width that also effects a fillet or a chumfer to a good view
its a layer production not a real part production from a pice of material

http://printwiki.org/Fillet

you shoudt make a quick Handsketch no matter it looks to get US all a better understanding of what you try to adchive

set hard hidden to true
then you will see the helplines ( Blue lines in Sketcher with there endpoints ))
there you can grap the line ends

a clean mesh solves the most problems on reconstruction
use Blender or at least the mesh clener here

do you got the sketch full green and the points tangential
you need to select the top face to make the corners champfer

SLAa or DLP is the best for things below double layer or nozzle sise to a working part there are onlineprinters that make this things very cheep if it is a real prototype 0,4mm noozle and 0,2mm layer will not work on that part as the fluctuation is very raw on that hight even with perfect filament a...

is this only with ubuntu a problem no windows user is reporting this things
mendy did yu try to reset with the commands the frame setting
while running freecad

ok understand
so
did you try
sleep 5 && compiz --replace;

or
compiz-decorator --replace

does this bring back your decobar

you may select the straight edges alone and make a fillet
then the arc edge this might work straight

kolona if you tell us what kind of baking mold you woudt like to see we cen do some more magic for you so i guess you are on the right way to do it as you now can get outlines and offsets if thickness does not work you can use sketch from face and do a offset there make a pad out of it and boolen i...