I've got the same problem. When I save a simple product or a product with variants (I only use these types of products ..) I get an error message with "Invalid or duplicated Supplier SKU." text.
There is the possibility that the Supplier SKU is the same in variable products, but for simple products the value entered is unique throughout the catalog ...
However the changes are ok it seems ...
I've this software version:
- WordPress v5.1.1
- WooCommerce v3.5.7
- ATUM v18.104.22.168
WooCommerce status page in pvt msg... leave me the email to contact you in private
Thanks a lot