LastSubmission alerts on state change, not event

Clients of LastSubmission care about the state of the submissions, not
the events that are triggering the state changes. For example, if the
'fail' event triggers the LastSuccess to enter the 'success' state,
clients care that there *is* a successful submission.
support showing an error state

An error state will appear on the Nexus Dropzone if there is an error
with a submission before any other submission complete successfully