Notification isn't picking up latest replies from users!

As the title say, I'm not picking up users in forums who replays to me and I can't pick up notifications at all and when I return later to the same thread, I saw someone reply to me but never pick up the notify from my mailbox.

This has been happening to me for over 6 months. I've started this thread before and so have several others. They wont/cant/don't know how to fix it.

Noticed that just now actually.