Look at this build: https://integration.mediawiki.org/ci/job/MediaWiki-GIT-Fetching/4730/console

(it uses Git and Gerrit plugins)

At some point it does an RPC, which results in a 503 (perhaps our Gerrit install was being updated or there might have been an intermediate issue). However nothing happened after that in Jenkins for over an hour. The build wasn't marked FAILED, it didn't (appear to) try again, nothing. No builds happened for over an hour because that build was stuck (we have parallel builds disabled).