The winning bid matches my maximum bid, why did I not win the lot?

There may be a tie situation. If another bidder places a bid equal to yours, it is at the auctioneer's discretion who is awarded the lot.

Also check whether your registration has been accepted by the auction house. You must be authorised by the auction house to place bids. It is possible that your auction registration had not yet been accepted at the time of the auction. For checking this status, here is another guide.