Maybe you haven't installed the correct plugin? The correct plugin is the YAML axis plugin

But we installed it:

Thanks for the reply. I see a similar failure when I try to use the YAML axis plugin with Jenkins 2.426.3. Steps that I took while trying to duplicate the problem:

1. Create a plugins.txt file that lists the exact plugins to install, including YAML axis plugin 0.3.0 and the most recent releases of related plugins
2. Create a run-jenkins.sh script that downloads Jenkins 2.426.3, the plugin installation manager tool, and the files listed in plugins.txt
3. Run the run-jenkins.sh script and complete the Jenkins setup wizard by choosing to install no additional plugins
4. Create a matrix project and attempt to add an axis. The only axis available is "User defined" axis. The YAML axis is not offered

Unfortunately, I'm not a user of the YAML axis plugin, so I won't be any further help here. You might consider debugging the plugin to understand why it is failing. You might consider bisecting Jenkins LTS releases to see if you can identify when the failure started. You might consider proposing pull requests to the YAML axis plugin to modernize it.

I am working with yossimerzbach on the same server.

We had it working and the problem started after upgrading from 2.263.3 to 2.426.3

The matrix plugin version is 822.824.v14451b_c0fd42

It is missing in an old job that existed before the Jenkins upgrade, and missing also if you create a new matrix project job.

https://github.com/jenkinsci/yaml-axis-plugin/pull/54

Is the issue resolved with the latest release?

Should be.

Can you please confirm?

I do not use this plugin. Can a user who is affected please confirm?

yossimerzbach will verify it next week (we are colleagues).