All products/variants were imported using WP All import, and all is well except products with only one variation. It was done this way because the supplier’s API is providing info about the products in form parent->variation, and there are many products that currently have single variation, but that is changing on a weekly basis.
It looks like manually entering the price and re-saving solves the issue, but there are too many products affected to do this manually.
I think this is a bug in Woocommerce..
