[Python] matplotlib creates "broken" filled curves made out of segments rather than a solid...

I have a fairly complex figure made with matplotlib. At some point, the code draws a "filled curve". With resolution of 100 DPI, the figure looks nice. However, by increasing the DPI, the filled polygons start to look as made out of horizontal segments, with 1 px void between them.

This is a crop of the original 100 DPI image (not the raw image, but takes as a screenshot)



And this is the same with 400 DPI (again, not the raw image but a screenshot with the same size as the former)



Why this might be happening? Can it be an artifact of the antialiasing algorithm?

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