I bid $31 for this item, only one bid was received according to the auction data, and they won it for $24.50. How is it that my bid was never placed? This has happened a couple of times now, either the item is won by someone else with a lower bid, with no record of my bid, or the item closes with no bids having not received my bid.

Hello Patrick,
Thank you for your question about this snipe. To see why you didn't win an auction, visit your "Completed" tab and hover your mouse over the error icon.
The error returned by eBay is: "Unfortunately, this seller has decided that you are not permitted to bid on their listings. You may contact the seller via the "Ask Seller Questions" feature if you want additional details."
Since this is happening with multiple sellers, you most likely have an account condition that is triggering the seller's Buyer Requirements.
This page may help:
https://www.ebay.com/bmgt/buyerrequirements
Please let me know if this helped. We're always trying to predict errors before they occur.