I have installed the just-released Monitoring Plugin 1.66.0. This version includes Real User Monitoring, which I enabled by starting Jenkins with -Djavamelody.rum-enabled=true.
However, I do not see the new statistics as expected. When I go to the Jenkins monitoring page, then in the "Statistics http system errors" section, I see many errors of the form:
So, it looks like RUM has indeed been activated, but for some reason it looks like it's missing that .js file. Is this a packaging error in the plugin?