After having the post-mortem session, create a report for this incident.
Tickets and links that dealt with this incident:
T208840: Monitor user reports about imaginary conflicts
T209012: Preview on a new site breaks and leads to loose of the site content
T209036: The title "Foo" does not refer to an existing page
Should be published here: https://wikitech.wikimedia.org/wiki/Incident_documentation