Had this time once more in the past, before the forum update - new posts would be made in threads I was following but I was getting almost no notification - just a random one every now and then...
When the forum software was upgraded, the problem stopped, but it manifested itself again several days ago... I'd say I'm getting 1/10 of the email notifications I should be getting.
Reality is that, which, when you stop believing in it, doesn't go away. --P.K.Dick