The Infant series of my Ysabeau typeface currently fails to export, citing this problem:
Of course, the glyph does exist, and as far as I can tell, the instance’s custom parameters should not destroy it:
Decompose should apply to all glyphs in the typeface so as to avoid unexpected component swapping. Remove features presumably does nothing to the actual glyphs? And Rename Glyphs contains this relevant line:
llinebelow.ss01=llinebelow
Both of these glyphs exist, so I don’t see how one of them could get lost.
I recently had trouble with /rlinebelow, which decided to rename itself /rmacronbelow unexpectedly, but llinebelow doesn’t seem to want to do that when I use Update Glyph Info on it.
The file is available here.