For some products, you can see the orders graph going down. As the number of orders is coming directly from Aliexpress, so it means there the number of orders is also going down. We think this is because only orders from a certain period are counted. When a product is on the site for a long time it means that older orders are not counted and you see the order graph going down. If you see an order graph with a downward trend it means that the peak of orders was in the past.
For finding trending products this is usually not a problem. Most of those products are not on the site for a long time. In case an older product that is suddenly starting to sell there are often just a few older orders, so the effect is minimal.