For some reason, happened twice already in the past week or so, I lost the biddings due to what seem to be either unsent or delayed snipes.
Would you help figure out what went wrong? I put my snipes comfortably above the winning bids, and eBay does not show my snipes at all.

Hello,
Thanks for your question. It appears that your authorization expired. This error is shown in your Completed tab. To remedy this, please go to BidSlammer Preferences and click the link that says "Refresh your Authorization."
Please let us know if we can answer any other questions.

Thanks.
How often do I have to refresh?

About once every 18 months. We need to put the expiration date on there. Thank you for bringing that to our attention.
Good luck sniping!