I’ve just experienced the same issue with an item sold 2 days ago. I have a Gmail account and have sold 3 items in the last two weeks. No issues with the first two, no email notification for the third (I checked Spam too). I emailed the buyer anyway, but as yet, have not had a reply (the buyer has excellent feedback) so I’m worried they haven’t received a formal notification either and may not even be aware they won the auction. I have since purchased an item and received notifications - it’s just this one auction that’s playing up.