New chain/old sprocket is classic for shipping.

With wear the rollers create pockets at the base of the teeth. That allows the chain to settle deeper and the next roller ends up bumping the corner as it meets the teeth. That causes it to climb up and ride the top, until the pitches line up tha the chain can engage. That's why you get the one link skip.

If the skipping is very minor and you can live with it, ride the bike, and the bumping roller will wear the offending corner, and the problem will solve itself. Or you can use a Dremel to break the back corners of all the teeth on the problem sprocket, and solve it immediately (but it's a slow process).