I only have two instances I can think of. i often buy engines from breakers on eBay. The last batch hasn't arrived yet and it has been over a month. One day the tracking said it has been missent, whatever that means. Now it says it is on the way.
The other time is when I was a kit a few years ago. I had ordered an Edsel Ranger kit from an ad on the back of a comic book. Never got it. Went to the post office everyday for weeks, always disappointed.