What did you set the notification Recipients parameter to in CB Activity > Parameters > Notifications > Article? It should be set to Article Owner to notify the article owner of comments on their articles. Sounds like it was set to Moderators?

Those are the relevant parameters. It's just a bug with their label being Mention. Will retest that notification to make sure article owner is working as expected.

Have re-tested the article comment notification and seams to work perfectly fine in my tests so I'm not sure what more to suggest.

Are you using a custom comment stream for article comments or are you using the one that was included in CB Activity? If you're using a custom stream and it doesn't have an asset of "article.[article_id]" then that notification will not work.

The way it should work is User A is the owner of the article. User B comments. User A is notified of the comment from User B. User C then comments. The grouping logic kicks in and merges the 2 notifications. User A is notified of the comment and it will state it's from User C and User B. That will only happen if the 2 comments are within 15 minutes of one another otherwise it will just create a new notification row for User C and aggregate them on display. Now if User B comments again it does not create a new notification. It simply updates the existing with a new date.

I'm out of ideas here other than implementing your own email directly off the comment trigger. Example as follows.

Global
Triggers: activity_onAfterCommentStreamCreate
Type: Email
User: Specific
User IDs: [var2_created_by]
Access: Everybody
Conditions
Condition 1
Field: Custom > Value
Custom Value: [var3_parent_id]
Operator: Equal To
Value: 0
Condition 2
Field: Custom > Value
Custom Value: [var3_asset]
Operator: Is REGEX
Value:
I've confirmed the above does work to email the article owner on comment.