During discarding the draft, the attributes are deleted first and without the transaction (https://github.com/ezsystems/ezpublish-legacy-ee/blob/master/kernel/classes/ezcontentobjectversion.php#L923 and https://github.com/ezsystems/ezpublish-legacy-ee/blob/master/kernel/classes/ezcontentobjectversion.php#L927 ; `removeThis()` method call is not wrapped in the transaction either). If the request stops right before the transaction or the transaction rollbacks, then attributes will be deleted, but version with the draft will still be there, which in turn makes the draft no longer editable (if you try to edit this version, then no attributes are shown, so there is nothing to edit).