Brand new Jenkins master. Go to Jenkins > New Item > (enter a name) 

Select "Multi-configuration project"

Click OK

Get a configure page. Go to "Configuration Matrix". Click "Add Axis"  Select "Label Expression". Click on that. Nothing. No new panel. Select "Slaves" Nothing changes. No new panel. Select and click on "User defined Axis". Nothing happens.

Go to old Jenkins master on another server,  (Jenkins ver 2.67, matrix project plugin 1.11), repeat the steps, try "Label expression" and get new panel, like I expected. Older one (Jenkins 2.33, Matrix Project Plugin version 1.11) is also good. 

I downloaded the 2.6 jenkins.war into the new server, replaced the 2.7.1 jenkins.war with the older one and the problem persists. Tried rebooting the server entirely and no change. 

I have a multi-configuration project on an older server. I copied the config.xml file into the new server, reloaded data from disk and see the user defined axis just fine, but the "Add axis" button still does not work.