USPS tracking isn’t so hot. I know what you’re talking about. I’ve received items and then days later, the USPS system shows them as being delivered. This is rare.
Also, certain areas of the country get bogged down by storms and other “extreme weather” and stuff just can’t be dealt with. Some areas are just plain slow. No offense intended, but most of the time whenever something heads my way from Florida, Texas or the other “Deep south” states, stuff just sits around for a while before even moving. I can get a package mailed to me FASTER from YYE than a yoyo retailer not 60 miles from where I live. I’m guessing most of the workers at the Oakland postal sort facility are on weed or something and that slows things down even further. Add to that the temporary holiday mail/shipping that is going on, and a system that is normally operating a fair bit UNDER maximum capacity is suddenly choking on its own proverbial vomit. This cold snap certainly isn’t help either.
First, contact the post office and see if they can advice what is going on. They could even try to put a trace out for your package. I’ve found this to be totally ineffective, but I would investigate that lead first. You do have some sort of delivery confirmation or tracking and that helps. I have found these issues tend to sort themselves out on their own though.
Second, you can ask the sender to do the same thing. Hitting it from both ends sends red flags through the system. It doesn’t necessarily speed things up, but a few more people have to get involved.
Last, Priority Mail isn’t necessarily 3 days. It can be up to 7, but 3 days isn’t unusual and 4 is fairly normal. 10 days isn’t unusual either.