Beginning with Gnome 3.26, the tray (aka notification area or system tray) has been removed from the Gnome desktop environment. That means that on a default installation, Gnome users will no longer see any application icons, SpiderOak One and Groups included. This is a Gnome decision and is out of our hands.
This affects distributions that use Gnome by default, such as Fedora and Ubuntu. It also affects users who have chosen to use Gnome as their desktop environment.
A workaround that is endorsed by the Gnome team is to install the Topicons Gnome extension, which restores the tray. The SpiderOak One or Groups icon will appear in it, along with all your other icons. This works on our own test computers as well as those of many of our users. Some of our users report that it does not work for them. We wish that there were a Gnome-recommended solution that is maintained, but again this is out of our hands.
If your only need is to shut down the SpiderOak One application, you can do that via any process manager such the Gnome System Monitor or your favorite command line process management tools.
A final workaround is to use a desktop environment that continues to have a notification area. All major desktop environments other than Gnome have notification areas. Popular choices include KDE and Xfce, and there are many more.