Transparent overlaping path when creating font with Illustrator and FontSelf

I'm trying to create a glyph font with FontSelf (https://www.fontself.com/) and Adobe Illustrator but I'm running into somes problems.

As you can see on the screen capture below, on the exported font, the overlaping path are showing as transparent as if they were negating each other ?

Screen capture of the finsihed font exhibing the overlaping paths problem:

I've tried to insert the shapes in FontSelf as outlined path, expanded shapes, coupond path. But in some case part of the illustration simply are not being imported in FontSelf, or they exhibit the "overlaping path problem".

What whould you guys advise ?

Thanks

Damien