Sometimes you'll see a blue banner on your build page indicating that there was an issue and the job was re-run automatically.
These issues are not related to your project. Sometimes CircleCI will experience infrastructure failures, and in these instances, we will try to automatically start the job again. If you would like to rerun the job manually as well, you can always rerun jobs from the UI.
If you notice this happening for an extended period on your project please submit a support ticket.