Clicking "Pipeline Syntax" in the sidebar and then "Declarative Directive Generator" works for a Pipeline, but not for a Multibranch Pipeline.  In the latter case, a 404 page is shown.

This seems to happen in all cases, regardless of whether the jobs are defined at the top-level, or within a folder, e.g.:

Fine:
- /job/pipeline/directive-generator/
- /job/folder/job/pipeline/directive-generator/

404:
- /job/mb-pipeline/directive-generator/
- /job/folder/job/mb-pipeline/directive-generator/