GitHub often has connection issues making the build fails for bad reasons.
The workaround we currently apply on https://qa.nuxeo.org/jenkins/job/addons-master/ is to rebuild up to 5 times, using "Retry build after failure", when the regexp ".*GitException: Could not fetch from any repository" matches the logs.

Such error could be easier detected by the GitHub plugin and the "retry" workaround being automatically applied.