I have also a strange issue. When i set swift page builder ON in product page, without adding any content with swift page builder, the first tab of description is NOT display only second and third like here http://www.loujett.com/shop/bijoux/bracelet-jonc-peau-serpent-de-mer-naturel-1-kayahnat1/

To fix this issue i have to add a fake swift page builder content (a text point), then the 3 tabs are displayed, like on all other product pages from the shop.

Hope it will help