I somtimes see fatal: unable to access 'https://github.com/llvm/llvm-project.git/': Could not resolve host: github.com
in buildbot log files, one recent example:
http://lab.llvm.org:8011/#/builders/131/builds/7
From looking at the documentation, the Git step supports also retryFetch, I hope this fixes these issues.
I can't test his as I do not have a running master instance.