"Pending sale" auction sales lost

I've put up large number of auctions over the last week, most of the sales come through to me normally - however 30% are getting stuck in my mailbox with 'Pending sale/pending amount' after item was sold buyout price. Sometimes these state "Amount available: <time>", however next day these letters are deleted and no longer in my mailbox, even the ones I did not click to view yet.

Is this a known issue or am I missing something here? Most of the items I'm selling are between 30-70G/ea so I don't like to think how much has been lost.

Thank you.