If anyone else has a similar question – I didn’t fully understand the question initially. Even though existing product notes were not disappearing, it was not importing new notes with the “Product/Review CSV Import Export” plugin (by WebToffee). This is now fixed in our plugin v2.5.2. Now there are new “Product/Review CSV Import Export” checkboxes in “WooCommerce > Settings > Product Notes > Private/Public notes > Compatibility Options” – when enabled, the import with the “Product/Review CSV Import Export” plugin works normally.