Red Forbidden sign on my glyph lowercase a +

Does anyone know what this sign means und I can mamage to undo it? Also with this sign the lowercase a is not in the normal array of gryphs. It appears after the lowercase z.

Thank you
Bildschirmfoto 2020-12-17 um 11.15.55

It means it is marked for not exporting. Right click and set the checkmark on export.

Great! Thank you