Just noticed this morning that when bulk uploading the "Variant Inventory Qty" values are not coming across. I have tested this multiple time this morning only to have the backend manager show "0" after a successful import that has the "Variant Inventory Qty" field populated.. not sure if this has anything to do with the backend UI upgrade you guys have done... this is a show stopper right now for us, so please assist.
I'm having the same problem. I contacted Shopify support who told me "I think it's due to a compatibility issue between the way the CSV is structured and the new locations feature which was released last year".
Other users have reported this may be due to having multiple "Locations" set. I noticed the problem first occurred for me when I added the Printful App which added a second location to my store. You can check your stores locations in Shopify admin Settings > Locations.
There is a new "Inventory" option in the "Products" menu. It offers an import/export option like the products menu. It seems you have to upload product inventory for each location here.
Since I dropship most of my products, I've got around this by simply uploading CSV's with "Varient Inventory" and "Varient Inventory Qty" blank for now.