Featured image conflict with selectable gallery images

Hello!

I’m trying the free version and this is the issue (I’ve posted both examples to show it):

When the product has a featured image, the selected image from the gallery does not appear in the preview: https://mydolliesestudio.com/producto/tarjeta-regalo/

Instead, if I disable the featured image, it does work: https://mydolliesestudio.com/producto/tarjeta-regalo-copia/

I’ve researched a lot, but haven’t been able to figure it out… I would appreciate any solution.

Thank you so much.

The page I need help with: [log in to see the link]