Unspecific message shown in Portal when a validation in "Create Issue" transition fails

Summary

When administrator adds an additional validator to the "Create" transition and user tried to create an issue (which is using the workflow with the additional validator) from Customer portal, the issue creation will fail with following error if user did not fulfill the validator:

Your request could not be created. Please check the fields have been correctly filled in.

Steps to reproduce

1. Edit the existing workflow used by a Service Desk project.
2. Add a validator (Eg: "Field Required" from JSU) to the "Create" transition.
3. Publish the workflow.
4. Try creating issue from Service Desk portal.

Environment

Jira Service Desk 3.16.0, 3.16.1

Expected Results

Issue creation failed by specifying field which is failed the validation.

Actual Results

Following error shown in Customer Portal:

Your request could not be created. Please check the fields have been correctly filled in.

Workaround

Remove the validator that requires the field on Create Issue transition on the workflow.