product images not showing in order

Site URL: https://www.lobeliabluecreativestudio.com/pinsandjewellery

I sell pins. my first product photo for each item is a close up of the front of the pin, the second image is of the back of the pin. for some reason on the shop page a few of the products show the second image as the thumbnail instead of the first (so you see the back first instead of the front) and I don't know how to fix it! I tried reuploading the first image but no luck. anybody have any ideas? thanks.

I have exactly the same Problem on a clients site. 

If there is a solution  - please let me know. 🙏

Website link: https://www.weingut-diehl.com/kein-wein-products

Hello there,

I hope you are doing well today.

Please disable any third party plugins that you may have active currently because one of these plugins may be preventing the image from appearing.

Please update me on the results.

Best Regards,
Oscar Jack