Notification on comments (3.1.5)

Since my admin updated Elgg form 2.X to 3.1.5  some great features are lost.

One major problem I experience is that when X writes a blogpost and I comment on that post I don't get a notification when any other comment is left to my comment. Notifications only work for new posts and comments to my post but not for comments to comments. Any chance to fix this or any advice on plugins? Since we use elgg for discussions, this is crucial for us. Thank you!