I purchased a few items at a grocery store a few weeks back. When I was going down though all of my monthly purchases I noticed the transaction wasn't there. I got a receipt for the items as well as cash back. The transaction is not in pending transactions or anywhere under payments. I added up my transactions and it is equal to the amount of my payments, so it didn't just get added to the total. Most of my purchases appear under pending almost immediately after purchasing the item and get posted a few days later. I called the credit card and they are not seeing a record of me making the purchase. Did I just not get charged for these items some how?
It's not that commonly known, but businesses are allowed to do what's called "Stand-in processing" or "Store and forward". This comes up when their connection to their credit card processor is down, but they don't want to just say "No one can pay with a credit card." Instead, their local system can say "I can't be sure that this card is actually valid, but it's low risk so I'll just approve it." (Low risk is defined by the business, and usually involves being under a certain dollar amount, chip cards only, or things like that.)
At a later point, after their connection comes back up, they send all those transactions off to the processor, which goes and hits the your bank for authorization like normal. Under most circumstances, this transaction gets approved, so the customer gets charged, the business gets paid, and it works out the same as normal (albeit possibly a few hours or a few days later than otherwise). On occasion, the card was actually fraudulent, or the customer just didn't have enough credit left, or something else goes wrong, in which case the business just loses that money. (There's also rules around retrying multiple times and various responses, but they're not relevant here.)
The system is generally designed to make it very hard for the customer (or even the clerk) to tell that it's "offline". After all, if you know that the store is down, you can commit fraud much more easily. I have even heard of businesses being offline for several weeks before anyone actually noticed.
To bring it back to your situation, I suspect this is what happened here - the connection from the grocery store to the processor went down, but you did a transaction that was small enough that they were willing to let it happen based on the (high) odds that you were a legitimate customer. Presumably, their connection hasn't come back up and/or they haven't replayed the stored transactions, so your bank hasn't been told about it yet. It should show up eventually, though.