Cannot get product image to display

Created my first inventory products today.

For the first product, the image worked OK.

The other 3 products, despite uploading several times, will not display an image.
I just get the standard “no image available” image with the Amazon logo.

The images comply 100% with the requirements here:
https://sellercentral.amazon.co.uk/gp/help/1881?referral=A265DNYM8JW2UU_A1FPORJSTN6AJL

When editing the product, each image is present in the MAIN placeholder.

However, just above the page says:

Live on Amazon
There are currently no images for this product.

I just cannot get them to display, even deleting MAIN and uploading again does not fix the issue.