Import stops working

Import was working for a while, when trying to import new products added to the woo-commerce store to Shopify, it shows running and complete, the log file shows import successfully, but cannot find the products in Shopify at all.

Recreated several new apps and still no luck.

We have about 400 products in woocommerce store and without variants. It shall not be the Shopify limitation issue.

Tried many time without success, very frustrated.