*I don't mind fixing this. *

If I understand right, this is the flow:
Going to statistics => an html page (/app/views/statistics/index.html.erb) and a json file are rendered (/app/controllers/statistics_controller.rb), with some help from helpers (/app/helpers/statistics_helper.rb) the charts are generated.
In addition to that, the charts use the function `search_on_click`(https://github.com/theforeman/foreman/blob/develop/app/assets/javascripts/charts.js#L233) to replace `~VAL1~` and `~VAL2~` with the appropriate values in the data-series.

This is my approach to fix this: https://github.com/ripcurld00d/foreman/blob/fixyyy_patch/app/assets/javascripts/charts.js#L233 and
https://github.com/ripcurld00d/foreman/blob/fixyyy_patch/app/helpers/statistics_helper.rb

By the way, I haven't tested it yet. Does anyone know how to test it "quickly" (just to see the logic is right)?

Best Regards.

Either from a git checkout or on a production install you'd have to recompile assets locally (install foreman-assets, then run foreman-rake assets:precompile & restart Apache).

Thanks Dominic. I will do that when I get home (on my production environment). If I see it doesn't break anything, I will push it as a PR (and then wait for a review).