Mkmk error: export failed

Hi, Glyphs 3 (3098) shows me an error when I try to generate the font:

Invalid digit “_”
Found in: feature ‘mkmk’, line 25.
I found no way to edit that feature, it is not visible in the features list.
Thanks a lot

It might be that you have a invalid glyph name that contains a _?

Yes, thank you very much, Georg.
There has been a glyph named “-_” in the font. I guess it is a remain of testing around with arrows and ligatures. It’s removed and now it works!