Login is not working on beta cluster sites, and all Selenium tests using authentication are failing as Selenium cannot login. The error is: "There seems to be a problem with your login session; this action has been canceled as a precaution against session hijacking. Please resubmit the form."
Successful build build #1911 triggered on Oct 10th at 20:31 UTC. It was for https://gerrit.wikimedia.org/r/c/mediawiki/core/+/251312/119 which is not merged.
The first build that failed with Create account error is build #1912. It triggered at 20:40 UTC for https://gerrit.wikimedia.org/r/c/mediawiki/core/+/838733
Both patches were for mediawiki/core so something broke around that time. That might be figurable by doing a diff of the consoles outputs.
The last successful build is build #1913 triggered on Oct 10th at 20:49 for https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/841191 which is not merged.