They are shown for me in 3.0.4 (3092). What Mac OS version do you use?
Macos Sierra 10.12.4 (16E195)
I just checked in 10.11 and 10.13 (my 10.12 broke). And it worked in both. And I don’t think I changed something in the mean time.
And there is one class that is shown. It might be that you have several classes without names?
Can you send me that file?
Yes. There is *.glyph font file:
I started making this font in Glyphs2.
At some point (when third-party developers adapted plugins and scripts), I continued working in Glyphs3.
After some update Glyphs3 classes are not displayed. Although previously displayed (I checked). Features. Probably a bug in the field for typing the name of the Class