When I right-click, the menu of widgets comes up briefly and then disappears, making it impossible to select an item such as “New Slider”. An easy workaround is to be sliding/dragging while you right-click. I believe I have the latest everything (JUCE, Projucer, and Mac OS X High Sierra).
I can’t reproduce this using the latest Projucer on High Sierra. Does it happen all the time with all projects? Can you try creating a new blank project and seeing if it happens there too?
I downloaded JUCE on another computer and it is ok there. I now suspect a problem with my old project files.