Mick.. we have had that complaint before... it seems to come and go for some. Not sure where the source is but it's been suggested that it may be your own ISP as much as being an SN issue. Another user with the same complaint received a couple of notifications one day that were months old.. so it seemed that they were sent but not processed..
Not sure if we can track this sort of thing.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)