Since updating the plugin (10.4.0 -> 11.3.0), the Warnings-NG plugin no longer reports issues as new.
Before updating, a typical log output would look like as follows:

[GNU C Compiler (gcc)] Obtaining reference build from same job (JOB_NAME)
[GNU C Compiler (gcc)] Using reference build 'JOB_NAME JOB_NO' to compute new, fixed, and outstanding issues
[GNU C Compiler (gcc)] Issues delta (vs. reference build): outstanding: 704, new: 30, fixed: 12

After the update, the logs look like as follows:

[GNU C Compiler (gcc)] No valid reference build found
[GNU C Compiler (gcc)] All reported issues will be considered outstanding

I am not familiar with the Warnings-plugin source code, therefore, the following should be considered a guess:
In this commit: https://github.com/jenkinsci/warnings-ng-plugin/commit/48b46c855d6d06230f5d1689f387bdbbd2567886
IssuesPublisher.java::findReference() was changed, and the following code was removed:

  .orElseGet(() -> {
      log.logInfo("Obtaining reference build from same job (%s)", run.getParent().getDisplayName());
      return run;
  });

I am not sure about the nature of the change and therefore cannot say if this is a bug or not. *

Was it on purpose?
Was it an accident?
Is there another part of the code that should have taken over the responsibility for this code path, which for some reason does not work for me?
I am curious, since I could not find any reports about this issue, and the first version containing this change released 4 months ago.

*) all I can say for sure is that it broke my setup.