Issue Summary

Script runner's validator fails to recognise updates (clearing field) following the enablement of the Modern Transition Screen Experience.

When a workflow transition is configured with a plugin (script runner) validator (e.g., "Field Required" or "Validate a field") targeting paragraph field, the validator fails to block the transition if the field is updated/cleared directly on the Transition Screen.

The validator appears to evaluate the issue's state before the transition screen updates are applied, rather than validating the new values provided during the transition.

Note: This is reproducible in the New/Modern Transition Experience (this is not reproducible in the Old Transition Screen experience - https://community.atlassian.com/t5/Jira-articles/Now-GA-try-the-new-issue-transition-experience-in-Jira/ba-p/2734436 

Steps to Reproduce

1. Ensure the New Modern Transition Screen experience is enabled for the site
2. Configure a workflow transition with a validator (e.g., ensure to keep the field empty if certain value is selected on another field) for the paragraph field via Script runner which has field empty validator. 
3. Take a work item that currently has a Paragraph field value. Note: The paragraph field will need to be using the legacy plain-text renderer. This isn't supported anymore, but there may be old fields around. 
4. Trigger the transition to open the transition screen. say Open to Done. 
5. On the transition screen type something into the paragraph field
6. Then clear the Paragraph field.
7. Click the transition button (e.g., "Update" or "Done").

Expected Results

The validator should identify that the Paragraph field is now empty and carry on the transition.

Actual Results

The transition doen't occur and fails with error message even though the field value is empty.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available