Since the mid-december update of libgdk_pixbuf-2_0-0 to version 2.36.1,
hexchat's tray icon is no longer visible in eg. xfce's tray icon area.

There is a related Debian bugreport #848615 at

  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=848615

which suggests that this due to a regression in the latest libgdk_pixbuf
reported here

  https://bugzilla.gnome.org/show_bug.cgi?id=776105

and also suggests that this fix to hexchat itself

 
https://github.com/hexchat/hexchat/commit/4c178782a779f013fafab476506f7d4dae372b8a

which is part of hexchat's new 2.12.4 release (which has not landed in
Tumbleweed yet) would work around the issue. I quickly built me a 2.12.4 RPM
but the tray icon remains invisible. I had to actively downgrade
libgdk_pixbuf-2_0-0 to version 2.36.0 from last fall to get the tray icon
working again.