I'm getting exactly the same issue, on templates that were approving fine yesterday...
Try this, add the attribute to a div and nest the h1 inside:
1. You don't need to close <meta> tags that are defining Marketo variables.
2. You are defining an incorrect variable...
<meta class="mktoImg" mktoName="Social: Image" id="socialImg" default="">
There is no such thing as a "mktoImg" variable. We only support String, Color, and Boolean variables.
You would specify an editable image element on a <div> or <img>
If you want to make the og image tag editable, you would use a string variable and then the user would enter the image URL into the variable area in the landing page editor.