importexport – SKUs duplicated in the export

I just started working at a company that uses Magento (I think it's a 2.2 version). I am familiar with some other e-commerce platforms, but I have little experience in Magento.

This company updates the products individually / manually at present, and I am making the transition to the CSV loads. When I export (System> Export), there are approximately 4000 SKUs where there is an instance / row of the SKU (excellent), but there are approximately 1000 SKUs where there are 2 rows with the same SKU. A row has the variable "store_view_code" blank (it is the same as the 4000 products that only have one row), and the second instance, has the "store_view_code" set to "default", and there is very little or no more. Data in these rows.

How do I delete these duplicates (those with "store_view_code" by default)? And how do I prevent products from being added with this "default" store_view_code in the future?

More information … If I upload data in bulk to one of the elements that only exists as a 1 row instance, a second instance of second is created with the default value of store_view_code.