This was a new one.
The name table should be build as if the font is not variable so it should match the default master. So Glyphs tries to find an instance that is at the same coordinate as the default master.
That is a very bad way of deriving the name. I have the name set in Font Info, first tab, first field. Why is this now all of a sudden not used?
EDIT: I can’t believe it, but you are right. I suppose apps will just have to use ID 16 instead.