Secrets may be accidentally printed in the build logs. Travis hide them in the logs masking them as [secret] every time that it finds a match with the provided secrets. See https://discuss.circleci.com/t/masking-secrets-in-output-logs/22231
We're currently beta testing thris feature. If you'd like to sign up to get early access, you can do so here https://forms.gle/e1ucYVaLZJ83Dvw76 . Otherwise, you should see this be automatically enabled over the next few weeks.