I've been making a few weapons for a short while now and I've found that a similar issue arises pretty commonly. This time I've noticed that when making a convex portion of a blade with an edge that sharpens to nothing, the curvature is lost and somehow flattened prematurely.
The blade is two-sided but there should be no clipping faces, I've already merged vertices and tried remaking the faces. I know that making more edges to join the outer and the inner vertices can resolve this, but it doesn't preserve the smooth look of the blade. I also noticed that this problem doesn't arise when only one side of the sword has the face that's causing the issue. This is blender 2.8