https://jenkins.ci.cloudbees.com/job/core/job/jenkins_main_trunk/rssChangelog is 488K with 940 entries, which seems excessive. This seems to trigger
JENKINS-10524 in some cases, and probably puts excessive load on the server and network. This URL also undermines lazy loading by loading all build records for a job.
I think the feeds should be limited by default to, say, 20 entries. (RSS 0.91 limited feeds to 15, but we are using 2.0, or Atom.) Clients which really want a full-length feed can ask for it explicitly.