I’m on a Mac, running OS X 10.10.5
I did try to restart SketchUp, and even did a reboot on my computer, but neither approach worked.
After that I figured I might as well try to reinstall SketchUp thinking that that would fix it, but that didn’t work either.
I did find a solution by deleting the shortcuts.plist file. . . . When I did the reinstall I just ran the installer again and selected the replace existing files button. Maybe in my case the plist file got corrupted (?), and I guess that file doesn’t get overwritten with a new SU install. I originally wanted to delete all of the SU application files before I ran the new Install, but there was confusion as to which files belonged to SU 2016, and which belonged to SU 2015, … and I didn’t want to loose any of the 2015 files just yet.