Hi there!
I have been having a problem with my Glyphs, when I type in preview, the letters show up as blank, but when I select preview text they are there.
I have also exported the font to test in word and the separate glyphs also do not show up in the font file.
Is it a multiple master setup? Then make sure the glyph masters are compatible.
Are your glyphs named correctly and have Unicodes?
This is probably a font cache problem. Read this please:
http://www.glyphsapp.com/tutorials/eliminating-font-cache-problems
For testing, please use the Adobe Fonts folder:
http://www.glyphsapp.com/tutorials/testing-your-fonts-in-adobe-apps