comments/notifications on photos - cb Activity and cb Auto Actions

When USER1 writes a comment on USER2.article.gallery.photo a notification is added in
BACKEND => CB Plugins => CB Activity Plugins => Notifications

If USER1 writes another comment on the same photo, no notification is added.

So a user can write several comments to a photo, but only the first comment results in a notification.

It should refresh the notification. As in the date of the notification is changed so it shows as new again. There's no reason to spam them with a dozen notifications for commenting on the same photo. As for what behavior allows for this it's the "Load By" parameter of the auto action. If you want it to create a new notification every time you'll need to make a copy of that system action and set "Load By" to "None".