I started using WorkRave on a Ubuntu 14.04 machine. It was working fine. When I tried WorkRave on a Ubuntu 16.04, I had problems. The system tray icon of WorkRave would not respond to any mouse click. If it does not display the right-click menu, there is no way to open its settings and change its configuration!
This seems to be a known bug with KDE Plasma 5, which is what ships in Ubuntu 16.04. This bug report is here. Until this bug is fixed, I do not see how I will be able to even use WorkRave on Ubuntu 16.04.