FB共享图像仅在第二次共享时正确

I'm using facebook share functionality on my site via the following anchor-

<a href="//www.facebook.com/sharer/sharer.php?u='<URL W/ QUERY STRING>'" target="_blank">

The thumbnail image for the share is set via a value in the query string.

Trouble is, when I share via the above link, facebook pulls the wrong image for the share.

This is in spite of the following:

The correct image is present in the meta og:image tag of the header
The FB debugger pulls the correct image and returns no errors.
When the anchor tag is clicked a SECOND time, the correct image is pulled and is correct from then one for that url

The behaviour can be reproduced here

attempting to share 2x( thus witnessing how the 2nd time works)

and then navigating to a different query string

and witnessing the same issue Any ideas on why this would be? Thanks