The OrderByBestDiscount sorting is affected by the lowest list price and base price among all available trade policies.

For more sorting-related errors, see this documentation.

1. Configure at least two trade policies listed in your store.
2. Create a base price for a SKU.
3. Create a list price for the same SKU.
4. Configure the <vtex.cmc:searchResult/> control on the product page.

There is no workaround in the Portal. However, you can add VTEX Intelligent Search to your store.