The Naginator plugin creates a link on the project's build page like the following:

Started by Naginator after the failure of build 2018-04-11-143326

Where "2018-04-11-143326" is the name of a build that failed and is hyperlinked to the build output.  The hyperlink is:

https://my.jenkins.unisys.com/view/Stealth(aware)/job/NFoS-Sysgen-Branch/1,070/

As you can see, when the build number exceeds 999 a comma is injected into the URL, making it invalid.