Most platforms offer shipping at different quality levels, from stable official channels down to cheap bulk routes that rely on space-filling cargo. The level behind a line matters more than the name on the checkout page.
Many USFans lines are suspected to run on the lower end of that scale: fewer scans, slower movement, long gaps with no updates, and parcels waiting for leftover flight space instead of going out on a proper run.
Before a parcel even leaves China, the whole shipment is often handed from one freight forwarder to another. That handoff adds more waiting time and is a common reason tracking goes quiet for days.
The frustrating part is the pricing. USFans often charges for these lines like other platforms price their stable mainstream options. You pay for something that looks comparable on paper, but the route behind it is usually lower priority and worse to track.
So when a parcel sits at the same airport scan for a week, it often just means it is still stuck in a slow bulk pipeline, not that it is lost. USFans own tracker usually does a poor job explaining any of this, which is why people use TrackUSF to follow the carrier side instead.