When personal data is processed at a facility of the processor that is not located within the borders of the EEA. Incorrect. The location where the data is processed is of no significance to the obligation to notify data subjects of personal data breaches.
When personal data is processed by a party that agreed to the draft processing contract but has not yet sign it. Incorrect. Personal data processed by another party than the controller without a valid written contract is considered a personal data breach. In the given situation however, negative consequences for the data subjects are unlikely. Notifying the data subject is not obligatory in that case.
When the system on which the personal data is processed is attacked causing damage to its storage devices. Incorrect. Damage to storage devices will make access to the data difficult or even impossible but does not imply illegal processing.
When there is a significant probability that the breach will lead to a high risk for the privacy of the data subjects. Correct. If there is a significant probability of negative impact on the data subjects, the controller is obliged to notify them of the breach. (Literature: A, Chapter 5)

Recital 170 mentions "Since the objective of this Regulation, namely to ensure an equivalent level of protection of natural persons and the free flow of personal data throughout the Union, cannot be sufficiently achieved by the Member States and can rather, by reason of the scale or effects of the action, be better achieved at Union level, the Union may adopt measures, in accordance with the principle of subsidiarity as set out in Article 5 of the Treaty on European Union (TEU). In accordance with the principle of proportionality as set out in that Article, this Regulation does not go beyond what is necessary in order to achieve that objective." Proportionality says that personal data should be collected according to the purpose of processing, that is, proportional, and data that will not be used for the purpose should not be collected.
Subsidiarity is a principle that says that personal data can only be processed if there are no other means to achieve the objective. Therefore, the less personal data used, the less the possibilities of violating privacy.