In type, I noticed that some curve points looked like they had 'kinked'.
But checking the Glyphs font master and the generated font, all was fine.
Strange thing is that in Illustrator the actual vector line is correct (no kink, in highlighted blue on the attached image) but the black-filled area DOES have a kink (see the version where I added a magenta outline - the circle indicates a kink).

It’s like Illustrator is rounding off the values of the point placements when rendering on-screen displays, but still preserving the actual paths (which are not seen when printed - just the rounded version).

Font sample is 60pt, image is counter of '6'.