For our Netflix OSS projects, build status icons don't update in our GitHub pages unless we clear the browser cache. An example is at https://github.com/Netflix/RxJava
I investigated with Michael Neale and we found that the HTTP response includes "Cache-Control:public", which is likely causing the problem. Michael verified that this problem doesn't happen with build status icons from BuildHive, because the HTTP rsponses from BuildHive don't include the Cache-Control setting.
I looked at the plugin code to see if this was an easy fix, but it looks like the HTTP response is generated somewhere in the Stapler code, which I didn't want to mess with