From the OP and subsequent posts it looks like you mean parcels coming into the country through the international terminal at O'Hare. Besides customs taking their time you have the worst possible USPS DC in the country located in Chicago. All throughout USPS they're having major issues with employee retention as the USPS has been a failing financial model for years and as such have shifted over to hiring a ton of temp employees. The union employees get paid better and take all their time off, also taking a ton of free "covid" time away from work. So USPS fills in all the missing employees with a constantly rolling crew of temps who come and go. In the meantime our packages sit on pallets on a dock waiting for some employees to show up and unload/load and get the packages moving. Once it gets away from a DC it moves along better. It's getting them out of the DC that's the problem. That's where mail/packages stack up and sit without being scanned or moved until they get to the trailer that has your package on it.
You can call and start an investigation. Your local post office will call you and tell you little more than what a track result will tell you bit they can tell you whether it's just sitting there waiting for someone to open the truck and start working it or if it actually can't be found. I'm sure it's the former, there's no employees to work your package.