Kern On

I tried generating a VF TTF using `fontmake`, but got a lot of these alerts `WARNING:glyphsLib.builder.builders.UFOBuilder:Non-existent glyph class public.kern2.KO_M found in kerning rules.` The `KO_` leads me to believe that KernOn is involved? Any experience with `fontmake` and KernOn?

Looks like Kern On originally wrote the kerning and kerning classes (kerning groups as they are called in Glyphs). I’d assume something got jumbled after that. Without seeing the file, or knowing about the process this font went through, it is difficult to tell.

Have you tried the “Clean up” functionality provided by Glyphs?

Haven’t tried the "Clean Up" but I will, thanks Tim.