I presume this problem comes from widthAdjust.fea where @FRACTION_GLYPHS = [fraction divisionslash slash.frac] get their widths zeroed for some reason. Guessing the reason is combining them with other characters, eg. threequarters. However as a nasty side-effect the standalone versions have zero width and look really bad.

I don't think this is expected behavior, especially that other monospaced fonts do not exhibit such behavior.

I came across this problem using Source Code Pro (Hasklig) for editing Go language assembly, using division slash U+2215 as a module path separator.