Hi
That's a problem that we didn't yet manage to solve. This comes from our OpenGraph support provided on article layout. Expect to improve this on next updates.
Meanwhile you can do it in an other way.
Open template parameters and go to "Advanced Settings" panel and add this lines on "Custom CSS code" textarea. Save and go to your article.
Toggle editor
screen.png
and add class "center" (see picture) to the paragraph that holds image.
screen2.png
Enable again the editor by clicking again on "Toggle editor" button and save.
Now it should overrule the floating position of div and image will be displayed on the center.
Hope this fill your needs.
Sorry of this do some work but we promise that this problem will be fixed as soon as possible.
Cheers