Thanks Matthias. I had a look at the error mails, but I could not find any errors. But it looks like in all error emails, the LLVM sources are updated to revision 321010, always with the same files changed. Maybe the script got stuck?
The only other suspicious message in the logs is a python warning when running Sphinx:
opt/venv/sphinx/local/lib/python2.7/site-packages/sphinx/util/requests.py:64: UserWarning: Some links may return broken results due to being unable to check the Server Name Indication (SNI) in the returned SSL cert against the hostname in the url requested. Recommended to install "requests[security]" as a dependency or upgrade to a python version with SNI support (Python 3 and Python 2.7.9+).