Okay this is indeed reported in the UI, but the trains-agent is running the experiment, and seems to be failing to clone the repository in question.
Seems like a "https" error, git is actually failing to clone the repository error: RPC failed; curl 56 GnuTLS recv error (-54): Error in the pull function.
Can you manually run the clone command on that machine ? I would guess there is some kind of firewall sitting in the middle of the https connection, and that is causing the git to fail.