GIFs losing animation after automatic cropping

I’m currently using the theme RT-theme 18. On my website, there are various product pages each with a photo gallery that can open up in a light box. I noticed sometimes the thumbnails of the GIFs are animated on the product page, and other times you have to view the enlarged version in the light box to see the animation. I would like all the images to be animated without having to open the light box.

After some investigation, I discovered that if the GIF is too big, WordPress will automatically resize it, during which it loses the animation. However, if you upload a small enough GIF, WordPress doesn’t need to resize it and the animation is retained on the product page.

So my question is, how can I find the maximum dimensions for the thumbnail without playing a game of guess-and-check?

Animation works on this page:https://www.terrellcreative.com/product-detail/lenticular-rectangular-keychain/

But not on this page (should be the second image): https://www.terrellcreative.com/product-detail/lenticular-oblong-keychain/