Hi @dancing_on_sunshine @Sika ,
Did you enable the "Price per Inventory" option globally?
If you did this before setting the prices for all your inventories within products, all the prices will be 0 except the Main Inventory that takes the price values from the original WooCommerce data.
Just try to disable the Price per inventory global setting until you fill all the inventory prices and, then you can enable it again if you need it.
Instead of using the global option, you can also, set the "Price per inventory" at product level.