Runners not picking up jobs after upgrade from 15.6.0 to 15.8.1

Today I upgraded from 15.6.0 to 15.8.1, and jobs no longer run.
Jobs are still created, via push, schedules or API calls, and they appear as “pending” in the various pipelines.
Runners can still connect to the gitlab instance, I can see this in the logs:

==> /var/log/gitlab/nginx/gitlab_access.log <==
10.32.98.26 - - [06/Feb/2023:10:34:43 +0100] "POST /api/v4/jobs/request HTTP/1.1" 204 0 "" "gitlab-runner 15.8.1 (15-8-stable; go1.18.9; linux/amd64)" -

==> /var/log/gitlab/gitlab-workhorse/current <==
{"content_type":"","correlation_id":"01GRK17RZTNHB5N333AQG2HSPM","duration_ms":0,"host":"git.ovea.com","level":"info","method":"POST","msg":"access","proto":"HTTP/1.1","referrer":"","remote_addr":"178.20.67.132:0","remote_ip":"178.20.67.132","route":"^/api/v4/jobs/request\\z","status":204,"system":"http","time":"2023-02-06T10:34:43+01:00","ttfb_ms":0,"uri":"/api/v4/jobs/request","user_agent":"gitlab-runner 15.6.0 (15-6-stable; go1.18.8; linux/amd64)","written_bytes":0}

I don’t see any errors in the logs, and I am unsure what to check for next.

In the meantime, I rolled back to 15.6.0, and all pending jobs magically started running.

Wonder if you might need to update the version on your runners manually.

What do you mean update the version on my runners ?
This runner is 15.8.1, it is the latest version is it not ?

Ok, found out "409 Conflict" causes Runner to not run any jobs, and give up checking for new jobs for half an hour (#4360) · Issues · GitLab.org / gitlab-runner · GitLab
I did have a bad advertise_address.