I noticed this issue on Xubuntu as well as Ubuntu Mate. Apps like Dropbox and HotShots would show a missing icon in the indicator (as in the image). The problem seems to be with Qt based applications and affects Ubuntu 14.10, 15.04, 15.10 and 16.04. Noticed the same problem on Voyager Linux 16.04 too. Here are some temporary solutions that work till the problem gets fixed. Continue reading Fix missing indicator icons on Xubuntu
If you have noticed many application icons do not show by default in the system tray (panel) in Ubuntu 12.04 along with Unity even when you minimize them (e.g. Pidgin, Dropbox). To enable the icons in the system tray you need to edit a particular setting in the gconf-editor. The cmdline way of doing it is:
$ gsettings set com.canonical.Unity.Panel systray-whitelist \ "['Pidgin', 'Dropbox', 'qbittorrent']"
To show all –
$ gsettings set com.canonical.Unity.Panel systray-whitelist "['all']"
The above command will enable Pidgin and Dropbox icons in the system tray. Similarly you can enable your favourite applications.
Another way to do this is to install Unsettings. Then start the application and go to the Panel tab. Add the application you want to show in the system tray in Systray whitelist.
This feature has been completely removed in Ubuntu Raring (13.04). The idea is that applications should be system-tray aware by themselves. There is an workaround but I won’t recommended it.