What might be the reason for not receiving notifications

Not a big issue, but it strikes me that I haven't received forum notifications of a few threads I started.
The last notification was a week ago. There is nothing in my spam box.
Note: threads have this arrow in blue circle "You will receive notifications because you created this topic."

=

The forum only notifies you about new things if you are away from the site for a while. (An hour, I think.)

It doesn't report any email bounces from your account, fwiw, although outlook.com has been known to silently throw away emails from phpBB, which might affect other things perhaps.

Thanks!
That must be the explanation then as I did receive a notification of your above reply.

I did visit the forum, read other threads.
However, I exited the forum, without having read the replies or notifications on my earlier threads as didn't have the time anymore.
This is how I noticed this 'missing' notifications.

Anyway, all clear now.

You'll still get notifications on the site itself, it just won't send you an email if you visit within an hour of them happening.

If look at the top-right of the page, your icon should have a blue number over it saying there are unread notifications, and you can click it to see the most recent ones, or click the link at the bottom of the menu to see older ones.