Popup fails on "Could not execute action [ViewWorkflowTransition]" in workflow Designer

Summary

When clicking "View Conditions" or "View Validators" or "View Post Functions", popup opens with a 404 error containing "Could not execute action [ViewWorkflowTransition]" and stack trace attached to this ticket.

Reproduce steps

Create a workflow with following name "C&B workflow" as a copy of jira workflow. Click "Design" on it, right click on "Start Progress" transition and choose one of the "View..." context menu.

Thx for your support,
Regards,

Vincent.