Apparently “Make Component Glyph” and “Generate Glyphs” doesn’t work well for glyphs variants like adieresis.ss01 when I use my own GlyphData.xml.
I have a.ss01, dieresiscomb and my own GlyphData.xml (without any reference to the above named, just for some symbols).
I tried Cmd+Shift+G > “adieresis.ss01”. But the new glyph remains empty. I hit Cmd+Shift+Alt+C, but the glyph remains empty.
After renaming the GlyphData.xml everything works fine. A glyphData file with just header but no entries is also OK.