When using the Flow Core Action: Send Custom Notification and selecting a Public Group as notification recipients only members added directly to the public group are expected to receive notifications.
When 'Grant Access Using Hierarchies' is enabled on a Public Group, users who are part of the group through role hierarchy inheritance (rather than being direct group members) are excluded from custom notification delivery. This is expected behavior in Salesforce. The following role-hierarchy-based membership reasons are excluded from receiving notifications:
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