Encountering problem with the Locks & Latches mechanism. When the jobs that block all other builds are running, blocked builds still occasionally post to an executor but don't build until the blocked builds finish. When this occurs, if Hudson picks up another change and fires off another build of the same project it queues it. However when the build blocking other builds finishes, the queued build goes and builds on a different executor before the original job request already farmed to an executor can start, and then the original job stays locked on that executor. Subsequent builds for that project will always queue and never build again while that executor stays offline even though it shows no activity (you can only see that a build is still on hold by going to the project and looking at build history where the faulty build is still building).

Hudson master has to be restarted to reset and clear things, because nothing else works.