Problems when adding more than 2 characteristics

This means that the data of the variants of the product is not correct in the database.

To fix that for that product, you should:
1. Delete all the variants of the product on the listing of variants that you can access via the button "manage variants" on the product edition screen.
2. Delete the characteristics of the product.
3. Save the product.
4. Add the characteristics again.
5. The system will regenerate all the variants automatically and you should be able to see the dropdowns properly on the front end.