Font works, but glyphs are not showing in Glyph Window in PS

I discovered one of my fonts is not displaying the individual glyphs in Photoshop’s ‘Glyphs’ window. Each glyph just appears blank. Likewise, when mousing over a letter to toggle an alternate glyph, the options are all blank. When the user clicks one of the blank options, it works. Just the previews are broken. Otherwise, the font behaves perfectly.

A customer notified me of the issue (which replicated on my end), so I figure I can rule out cache being an issue? Any ideas?

Greg

Can be anything. Path directions, vertical metrics, complex paths, also caches. Are you using the Adobe Fonts folder for testing?
http://www.glyphsapp.com/tutorials/testing-your-fonts-in-adobe-apps