Media within the site updates just fine, but the default image does not update immediately. In fact, after pulling my hair out and giving up, someone noticed it had updated ... 4 days later!
So just to be clear, if I post our main web address in LinkedIn, it automatically includes the old image. Likewise, if I use an embedded LinkedIn share button on a blog post, it automatically includes the old image.
We are using an SEO plugin called Yoast, and a performance plugin called WP Rocket. First I tried to turn off the social media logo stuff in Yoast SEO and put og calls directly into the <head>. Next I tried to use WP Rocket's Clear cache option. Neither gets the new image to get used.
If I View Page Source on our site, it lists the correct image. If I FTP in to the site, the correct image is in the correct path. And if I browse straight to the image, it displays the correct image. It's only the automatic image posted to LinkedIn that seems to be cached somewhere.
I also tried to set the new image as the Featured Image on the blog post, but it's still getting overridden by the default, old, image.