About 20 minutes ago, I followed the console links of the last three builds for [this Gerrit change](https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/869185) (patch set 3) from Zuul; in two of them, I got an error like this:
{F36194089}
After reloading, I could view the logs as usual.
Possibly related upstream docs: https://docs.cloudbees.com/docs/cloudbees-ci-kb/latest/client-and-managed-masters/instance-navigation-often-fails-with-crumb-issuer-errors
Which says:
> In some environments, this check would fail and causes `No valid crumb was included in request`. For example when a proxy is not preserving the client IP or the `X-FORWARDED-FOR` header is set but mis-configured
On the Jenkins server side:
```
Jan 13 16:10:43 contint2001 jenkins[17543]: WARNING: [hudson.security.csrf.CrumbFilter doFilter] Found invalid crumb xxxxxxxx. If you are calling this URL with a script, please use the API Token instead. More information: https://www.jenkins.io/redirect/crumb-cannot-be-used-for-script
Jan 13 16:10:43 contint2001 jenkins[17543]: WARNING: [hudson.security.csrf.CrumbFilter doFilter] No valid crumb was included in request for /ci/job/quibble-vendor-mysql-php74-noselenium-docker/76991/logText/progressiveHtml by Lucas Werkmeister (WMDE). Returning 403.
```
And there was a second request for /ci/job/wmf-quibble-selenium-php74-docker/15950/logText/progressiveHtml which had the same token given. That matches the two tabs which were opened when the error happened.