Comment # 2 on bug 934162 from Raymond Wooninck

Given the user is using Tumbleweed, all KDE applications definitely switched to
Plasma5, which also has the switch regarding the systray icons.  Plasma5 is no
longer Xembed based, but on StatusNotifier. 

My guess is that XFCE4 for the user is setup that the systray only shows the
XEmbed based icons in its systray.

Googling delivered me the following post for Xubuntu that describes a similar
issue:  https://pseudomorph.wordpress.com/2014/05/08/xfce-notification-a/

Of course the solution described here will not work for the user, but replacing
the Notification Area applet with the Indicator Plugin applet should restore
all required items. 

I do not know if the Indicator Plugin applet is part of the openSUSE XFCE
desktop, but this is not a KDE/Plasma bug. Apologies for reassigning the bug
back to the XFCE group, but there is nothing that can be done from a KDE/Plasma
perspective as this is working as designed. XFCE System Tray would need to pick
up those icons that are using the StatusNotifier (which apparently can do
through this Indicator Plugin Applet).