How and by what do you import your data to Shopify? If you used CSV files to do it, please check whether file format is correct with Shopify. Or you have another option is that using an automated migration tool to helps you to correctly import data from CSV file to Shopify. I recommend you to use the Litextension tool for this process.
This is a reliable and popular service in terms of shopping cart migration, there are so many good reviews about this service and product on its FB and other forums. You should try free demo with a limited number of entities (20 entities) first to preview how easily the tool works, then contact the experts team via live chat on its website, they are always answer your questions really fast, if you still consider about the migration process or anything related to the migration.
Greetings of the day!
We would suggest you giving a try to Cart2Cart automated migration service. The tool has been developed to make the eCommerce migration across various shopping carts as seamless and error-free as possible.
The list of entities that you can transfer to Shopify includes products; product images, tags, variants; custom fields; product categories; product images; manufacturers; taxes; customers; orders; coupons and other related data. What's more, if you want to make your Shopify conversion even more seamless, you can take advantage of Additional Migration Options (like migrate customers groups into customer tags, preserve order IDs on new Shopify store, create 301 redirects after migration, etc.).
Feel free to contact us with any migration issue and we'll do our best to bring you the highest service level we can.