Created attachment 219664 [details]
Jenkins log file
Jenkins seems to be shipping with an old address somewhere for getting plugins.
I saw the same issue on another, previously working Linux server as well. After updating Jenkins itself, the instance on the Linux server started working again. The latest version in the FreeBSD repo doesn't work.
The FreeBSD instance is a fresh installation.
The Jenkins log has many exceptions like this:
java.io.IOException: Server returned HTTP response code: 503 for URL: https://get.jenkins.io/plugins/workflow-scm-step/2.11/workflow-scm-step.hpi