For the past 2-3 days, no web notifications or email notifications have been coming. To figure out more into this, here is the snapshots Settings -> Notifications.
In the above snapshot, no sub-options in the form of check boxes are appearing. Earlier it used to appear. In the snapshot given in the question, all sub-options below the heading
You've unsubscribed from emails about: are there.
Even when the email notifications is set to all notifications, it still shows
No notifications, as evident from the below snapshot.
In this regard, a form regarding notification issue was submitted to the Facebook, but this doesn't guarantee a response from them.
Here is snapshot Settings->Notification of a friend's Facebook account:
There are 169 items below
You've unsubscribed from emails about:, which is nowhere to be seen in my Facebook account's Settings->Notifications.