I think for us to properly help with this, you’ll have to share the build link. If you don’t want to share that here please email it to us at support@buildkite.com and we can discuss it via email instead.
In general, this status code usually happens on the elastic stack when the agent is taken away. Reasons range from spot instances being reclaimed to autoscaling reducing instances (although that shouldn’t happen while an agent is running a job). To know for sure though, we’d need to look at the build.