This is a very simple character so I am not sure what the issue could be:
Does it work with other glyphs?
It’s a different error message everytime. Sometimes C, H. Sometimes “notdef”.
I’m also getting an error message when I update in the Font Info > Features panel. " There was a problem converting the PostScript source font. (temp)"
Also not able to test any of my glpyhs or stylistic alternates - this error icon showing up in the bottom left of all letters.
Then you have the same problem them Export and Features error