Icon cache is always out of date on Windows
I am on MSYS2. Running any GTK3 application with GTK_DEBUG=icontheme shows lots of messages:
look for icon cache in D:\msys64\mingw64\share\icons\Adwaita
icon cache outdated
look for icon cache in D:\msys64\mingw64\share\icons\hicolor
icon cache outdated
But running gtk-update-icon-cache (even with -f argument) does not solve this.