It’s apparently a bug in Luban… 
I just copied your settings for a simple oval (using Luban’s add shape tool) aaand… it does the same thing. It does this (I assume) to remove the cusps left over from sweeping left and right, this was on the latest 4.3.0. However, on Luban 3.15.2, it only sweeps back and forth, it does not go back to do the outline, but you don’t get a fine edge, unless you do a secondary path to follow the outine, which actually gives you the result of sweeping back and forth to clear, then running along the outside in a smooth contour.
Your best option would be to use a different CAM software, a popular one is Fusion360, I have a two-pass guide here:
While it’s specifically for multi pass 3d engraves, it does have a section good for setting up Fusion for the snapmaker. You would simply want to import the SVG, then use the 2d pocket operation to fill it instead of all the other nonsense. 
Another option would be Kiri:moto, while I have not used this personally, I’ve read about others using it, and TeachingTech mentions using it in their review of the snapmaker. It’s free and browser based:
There’s other CAM software out there, but those are the ones I know of offhand. Sadly, it’s your best option, as Luban is just… sort of junk. You COULD install the older version, 3.15.2, do a fill operation, then add another for outline or on the path to do the edge and it would be a lot faster than the odd dance Luban 4.3.0 is giving you.