I am having the same issue. I do not have any themes or apps installed at this point in time. The 4th thumbnail image is showing up as the main product image. I have tried re-organizing my images, but no matter what image I use as the "large" main image, the same image always shows up on the product page as the main one. Has anyone found a fix for this?
I was experiencing the same issue.
It seems that shopify shows the variant image that is selected, instead of the featured image.
Try follow these steps, to see if it helps you out: https://shopify.dev/tutorials/customize-theme-show-featured-image-on-product-page
Hello, I am a store owner, and I have faced this problem too. The good news is a figure out the solution. This problem is caused by 2 main reasons; you did not make the default photo correctly, or the problem in the (variant section). To get to the hoping result please continue reading...
1- Move the photo you want to use as default and put it in the first-big square. (It will appear bigger than other photos).
2- If your product has more than one color/style/size, the variant section will display the photo of the determine color/style/size. To solve this you have to add a Fake-Variant. To do this you have to scroll a bit down the media-section and look for "Add Variant", press on it and set a new variant, and give it a name like (pick style) or (size) or (choose), finish, and save. Then go back to the "Variant section" and press on "Reorder Variants", then grab your Fake-Variant and put it first.
I know I spoke a lot but believe me it's so easy and effective, just follow the steps.