Unfortunately, it’s the same image, uploaded at the same size. Nothing different.
Still, I tried it again, but the same thing happened.
Also, I’ve noticed that if I don’t have a Featured image set on the blog page, the page doesn’t default to Homepage Header image, even though I have it set to “Enable on: Entire Site, Page/Post Featured Image”. Instead, it’s blank. Not sure if that’s related to my main issue of the wrong size image, but I’m mentioning it just in case.