Icon missing in systray

I can't change the settings of touchpad indicator, because there is no icon anymore in the systray (ubuntu 16.04 LTS).
without the icon it seems impossible to access settings. touchpad indicator is running, though.
I assume it's because I checked the option "start minimized".
but maybe it's because of updating ubuntu.
I tried uninstalling and reinstalling but the icon didn't reappear.