Product Gallery

I have a product with 1 featured image and 3 gallery images. On the product page, there’s a problem with the small images under the main image.

After the page loads there is only 1 small image shown under the main one. Then another one scrolls in, then it is gone again … after some time there are actually 4 images shown under the main image, but only for a few seconds.

2 screenshots (combined in 1 image): https://ibb.co/FKSJVHj