Which font is in use?
You can check to see if the 1/3 char is available for this font using Window's Character Map. Select the font, and search for "fraction" in the search box. You'll see the supported fractions. If there is not one for the font, and you want the 1/3 char, you'll have to either change fonts to one that includes this character glyph or supplement the font with your own 1/3 char.