This issue comes and goes, for many months:
*** Occasionally, I don't get notification of someone's reply to my comment or post, either in "Feeds" or in "Comments" section of pages.... I only know this, if I happen to see the reply by accident.
*** The number of notifications on the "Bell" , go up and down randomly, this has been happening for many months:
For example, today , I had notifications of "10" replies on the Bell, when I click, the number went down to "7", as the page w/ the comment opens, the number went back up to "8" . This repeats w/ every reply I select/open, the number decreasing each time, but also randomly. Towards the end , "3" was on the bell, I click and see there are more than 3 notifications left unread, I checked one by one until there 3 left ( 2 old ones, see below), as the page w/ comment opens , the Red box on the bell disappears, yet if I check, there are still 2 notifications there (see below).
*** Sometimes, although I have checked all the specified notifications, 1, or 2 or 3, will still remain under the bell, although the Red Box has disappeared; occasionally however, the red box remains w/ the numbers 1, 2, or 3, as if I had not opened/checked them at all. This remains, although I had clicked on that old notification again.
For example, 3 days ago, the last notification I checked, remained there (no red box on bell). The next day, it still remained, but now the last of the new batch remained also. Today, after I clicked on them all, the oldest, from 2 days prior disappeared after I selected it, but the one from yesterday, and the last one from today, remain, although there is no Red Box on the bell.
===>>> Obviously, the important thing, is that I get a notification if someone replies to any of my comments or posts.
Also, I no longer get notification if someone replies to the same post as I. It could be a newly implemented feature I am not aware of. If it is not, then that's an additional problem.