I just send a crash report about a crash when using the instance selector pop-up in the preview area.
In Glyphs 2 I get in this popup the complete style designation, preceded by the Family name (which may be a custom parameter in the instance definition).
In Glyphs 3 this is without the family name, and if the export name is long, only the start of it. If the export name is short, it is followed by (null).
There is also an eye in every entry. I suppose it is intended to show which exports are active. Many exports are not active in the file I looked at, but all eyes are black.
3033 on Catalina