Hi!
The artists are not showing up, because their age and gender is not set on the editor screen: https://i.imgur.com/wKe05qw.png
If you still want to include artists that does not meet the filter criteria, because the field is not set, you can enable this option: https://i.imgur.com/ACHJd5t.png
The slider handles were a visual bug, I have changed the filter layout from column to flex, now it should be visible and working.