Introduced with JENKINS-56510, when selecting "Warnings Plugin Native Format" as "Tool" the "Warning NG Plugins" should import an xml exported by the API:

<jenkins server>/job/<job name>/<build nr>/<tool id>/all/api/xml

The problem is that this API exports the report of issues as:

<reportApi _class="io.jenkins.plugins.analysis.core.restapi.ReportApi">
   <issue>
      <!-- .. -->
   </issue>
   <issue>
      <!-- .. -->
   </issue>
   <size>2</size>
</reportApi>

And the plugin expect "report/issue" as xmlIssueRoot (sort of x-path query) to find the issues.

In other words this can be imported:

<report _class="io.jenkins.plugins.analysis.core.restapi.ReportApi">
   <issue>
      <!-- .. -->
   </issue>
   <issue>
      <!-- .. -->
   </issue>
   <size>2</size>
</report>

The issue is that the root element is called reportApi in the exported xml and report is expected for the import

Tested with version 5.1.0