To force close a session using Windows 10:
On Windows. right-click the minimized Citrix icon and choose Advanced Preferences
Choose Connection Center
Highlight any open connections, and choose Log Off.
Rebooting the computer should close out any hanging local Citrix files.
To force-close on a Mac
On a Mac, look for the open Citrix Viewer icon
Right-click and choose Close
It should prompt you with Cancel, Log Off or Disconnect
Choose Log Off to force-close the session on the server.
If Citrix is hanging on the local workstation, hit Ctrl-and right-click the viewer and Force-Quit