"Track Inventory" Intermittent when bulk uploading

Dawn Theme. I’m uploading products using Shopify’s bulk (CSV) uploader without any problems really, but I’m finding that intermittently the “track Inventory” isn’t being checked (in approx 30% of items). Everything I upload has a positive inventory.

This is a function that I really need, is there an option to set this as default, or can anyone explain why it’s happening?

TIA