What you’re seeing is the slicer telling you that the resolution of the model is below that of the extruder setting. So let’s say you are using a 0.40 extruder but you’re trying to extrude a 0.04 line. The slicer will simply not render those lines.
You can try to increase wall loops and/or thickness and see if you get a different result.
Aren’t rc planes supposed to be printed in vase mode? I think at least the gaps (if you mean the crosses) are there to add internal structure.
The overshooting seems to be the trailing edge of the wing being too narrow. If the designer didn’t put a nice fillet there but a very sharp edge it will create a single line add-on which in this case will turn out ugly/weak. You can also play with the wall generator:
And enabling/disabling detect thin walls to see if it eliminates the “overshooting”:
The last setting is not always available depending on the first. Good luck!