Your package could be stuck in transit for many reasons: loss, damage, or even a USPS tracking system failure. More likely, though, the short-staffed US Post Office has misplaced, mislabelled, or simply overlooked your package. This means it can be located easily enough once you call attention to its absence.
UPS is typically pretty quick, but keep in mind that USPS can often take up to 24 hours to update tracking statuses. There are a few reasons why your package status may not be updated right away: If you drop your package off after hours, USPS or UPS won’t scan it in until the next day.