I think I figured out why this failed on occasion for me. It's when the iCloud Drive app hasn't yet downloaded the file but it's passing it to the app anyway. I don't know why iCloud Drive would do that, but that seems to be the only case that's failing.
Ligatures are powerful but underrated. Using ligatures, a word can be associated to a font glyph. You can download IcoMoon's free ligature font here. Both Essential and Ultimate packs come with their own ligature font. 2b1af7f3a8