A couple of times on this project the desktop on the data manager has gone black. It looks very disturbing if no other windows were open, because except for the mouse pointer on the screen, it looks like the desktop or the monitor crashed.
The workaround is to restart the plasma-desktop program like so:
Alt-F2 to open the run dialog, or use a terminal window. Run 'plasma-desktop'.
The plasma desktop should restart, and all the desktop background, icons, and toolbars should return.
There is a JIRA issue for this: https://jira.eol.ucar.edu/browse/ISS-555.