Reduce image size in some images on mobile

Hi,

I was testing this plugin on my staging website and all was great until I found this weird behavior on mobile: some images get their size sharply reduced.

1) Here′s a screenshot of an image with its normal size
2) Here′s a screenshot of an image with its size really reduced

It′s the same product and the images all have the same size.

You can see that they all have the same size, as you can see them on the production website: https://www.chefpanda.pt/produto/bolo-de-21-anos/

Do you know what is the reason that leads to this behavior?

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