When I open some SE site I usually see in my inbox notifications about new posts.
I noticed it already several times that not all new comments are notified. I clicked on my question and found out there is a new comment which I wasn't notified about, I looked to the inbox and it wasn't in history.
Is this a bug or is it normal that not all comments are notified? Due to this feature the communication can get stuck.
The question (the only one I can now refer to) may be deleted soon (I flagged it as duplicate). This one. I wasn't notified about the comment under it and two last comments under the only answer.