There is a known bug in webkit-based browsers (Chrome, Safari, but not Firefox) that prevents javascript from opening the same link to a new window or tab more than once.  This meant that you could only open a plot once and then any other attempts to open plots would fail silently until you reloaded the VPCsim page. The published workaround is to append a random number to the url.  It solved the problem.
There is a known bug in webkit-based browsers (Chrome, Safari, but not
Firefox) that prevents javascript from opening the same link to a new
window or tab more than once.  This meant that you could only open a plot
once and then any other attempts to open plots would fail silently until
you reloaded the VPCsim page. The published workaround is to append a
random number to the url.  It solved the problem.

aduffy70/VPCsim-Unity