Hello,
Did you check the image size before uploading the image to your library?
I checked one of the images that you used for that product https://prnt.sc/1gjtt4k – 4.1Mb just one image. You have up to 8 images for every color. So, do you understand the size of your page in this case and the loading time of all these images? Optimize images to 200-300Kb max before uploading them to your Media library. Read this post https://www.wpbeginner.com/beginners-guide/speed-wordpress-save-images-optimized-web/ it would help you to understand steps of the image optimization.
Also, if you remove images from the Media library, remove them for the variations because in this case, you have a broken list. We’ll try to improve this in the next theme update but now you need to clear the images gallery manually if you remove media.
Check the gallery thumbnails slider now.
Regards