I have now lost two items due to my bids not being placed by the app. It is up to date. On the first day I used it it worked but day 2 I lost an auction that ended at a bid lower than my sniper and the 3rd day same thing. I made sure to save the sniper twice each time.
Sniping does not guarantee winning. You have to meet eBay's or seller's requirements too.
You can always check what exactly you did not meet by checking the "My Status" field of your snipe.
If you want me to check it for you, please include the item number.