Can anyone tell me why the first image is NOT centered in this post, even though it says it is?
I think it has something to do with the caption, but I'm not sure what.
Your link displays a message that says "NEW SITE COMING SUPER SOON!"
You should be able to see it now.
You have an element style on the image setting the width at 640px, this is disrupting it from displaying properly, remove that and you should be okay.
(The actual width of the displayed image is 630px, that's why it there was that extra 10px pushing it off center)
Something like this is related to that specific image, so check where you have that one pic inserted into your post content. Perhaps the WP Media screen, that shows the title, caption, etc for the image and make sure nothing is set to 640px.
The key is to find the 640 px somewhere. You can do a css override for that ID, but it would be best to find the root of the problem.
Looks like you got it adjusted from 640 to 630, seems to be centered now, does that solve your question?
It's not ideal, as there is a backlog of hundreds of posts. But I'm dealing with it.