When there's failing task (Script task in this case) at the beginning of the process, then start of the process fails with two consecutive error dialogs.
Unable to complete your request. The following exception occurred: "Unable to create response: [errorsConsole.processErrorAtStart:9 - Process Error:2] -- On purpose".
which is expected.
An unexpected error happened. Please try again in a few moments.
which seems like the error is not caught and bubbles up to UI.
In the error details there's raw stacktrace of the error (from the Script task).
It looks like a regression, previously there used to be an 'Error' dialog with more info provided:
Unexpected error occurred: Unexpected HTTP response code when requesting URI 'http://localhost:8080/kie-server/services/rest/server/containers/consoleErrorsContainerID/tasks/2/states/completed'! Error code: 500, message: "Unexpected error during processing: [errorsConsole.processError:8 - Process Error:3] -- On purpose"