Figma SVG import issue icon turns to ALL BLACK


The left is what I draw in Figma.

The front-end developer downloads the svg, uploads into the icon library, then it turns to all black.

It is quite often to meet such problem.

The icon has been flatten well in Figma. I redraw the icon in sketch finally, then the problem disappear.

Anyone knows why? And how to avoid such problem? I don’t want to draw any icon twice.