x11-themes/adwaita-icon-theme-3.24.0 is installed and selected in xfce4-appearance-settings.
However there are icons missing like
..all icons on the right side are missing like Edit or Remove.
For instance Tango icons are working:
Btw. there are other oddities, x11-themes/yasis-icon-theme-0.4.2 has the Panel dialog icons complete, but has missing all directory and file icons in Thunar.
You can investigate the installed files in order to track down the problem in the meantime: