At first, the build was unstable (for which a mail was sent).
The next build failed.
However, the email we received stated that the build was "back to normal".
The build is configured to send the mail as the 2nd last step. The last step is the "Emotional Jenkins", which does not affect the outcome of the build (failed/stable).
No recent updates and I have not seen this issue before.
Attached both mails and a screenshot of the build numbers (unstable and then failed)