I've been periodically having images not loading and instead showing a small black box with a white X inside.

This is extremely frequent when I hatch eggs.

I've been having this issue too.

Because of how the new image builders work, I'm wondering if it's because the image is being accessed before it finishes saving to our server's disk.

Not much I can do about it at this point, though. But it'll be something I keep in mind and maybe will think of a workaround.