While creating instances, Cloud-init stops before creating the SSH keys

We have OpenStack v2.3.1, Mitaka with KVM installed on our cluster. While creating instances, the VMs are created successfully every time. However, Cloud-init randomly stops before creating SSH keys only on a few of the instances (this is not dependent on the node running the VM). Therefore, we cannot SSH to the created VM. This strangely does not leave any errors behind in the logs. Any idea what could cause this? Logs of working and non-working instances include below (The differences are at the end of the logs): Thank you.

A log of NON-Working instance on gist.github.com

A log of Working instance on gist.github.com