Gtk-WARNING **: Error loading icon: Couldn't recognize the image file format

Many GTK based apps failed with errors like:

Gtk-WARNING **: Error loading icon: Couldn't recognize the image file format for file '/usr/share/icons/oxygen/16x16/actions/application-exit.png'

until I ran this line to regenerate the cache:

gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache