Default title error in bulk product upload

Some of my products are displaying ‘Default Title’ instead of the variant product size.

I’ve uploaded products using the .csv import where Option 1 name = size and Option 1 value = various pot sizes. I can’t seen any problems with the data in the .csv and there doesn’t seem to be anything obviously different between the data for the products that are displaying correctly vs the ones that aren’t.

I’d appreciate any advice or assistance.

cheers