I just got a notification with missing username. Screenshots attached of notification area and also the database entry.
Database entry in social_notifications has COM_EASYSOCIAL_LIKES_INVOLVED_SYSTEM_TITLE in the title column and {"aggregate":true} in the params column.
Database entry in social_notifications has COM_EASYSOCIAL_LIKES_INVOLVED_SYSTEM_TITLE in the title column and {"aggregate":true} in the params column.