spurious horizontal contour lines depending on number of contour levels

I'm seeing an issue where spurious horizontal contour lines appear on my map depending on the number of contour levels I choose. I can also make the horizontal lines go away by 'zooming out' or broadening my plot domain.

Here's an example that has more contour levels and shows the problem (note the two horizontal lines, one near middle of plot, one near bottom):

And here's an example that has less contour levels and the problem goes away:

首先使用不同数量的等高线级别和绘图域复现报告中的地图，并以链接的两张示例图片作为视觉参考。追踪负责生成水平线的等高线渲染入口点；当多余的线不再出现且有效的等高线仍然保留时，即表示完成。