Hi there, @janjesant,
Is it the first time that this happens to your posts when sharing from your blog to facebook via Jetpack Social?
I suspect that this issue could be caused by a plugin conflict. For sharing to Facebook your posts must have valid Open Graph meta tags. You can find more details about that on this page. For Facebook, you can use Facebook’s Debug tool to see if your site has valid Open Graph tags. Jetpack will normally output those tags for you in your site’s source. It’s possible that the All In One SEO plugins have overwritten Jetpacks.
Since Facebook will give an error if there are duplicate Open Graph tags, Jetpack automatically deactivates its Open Graph tag generation when it detects that another plugin is adding them. Since I guess you’ll still want to use that SEO plugin but not their Open Graph output, you can use this plugin to force Jetpack to output its tags: Always Use Open Graph with Jetpack.
Let’s see if we can fix that by doing this. Please also notice that while Facebook depends on the Open Graph tags to choose which image it will display for any shared post, there is still a chance that Facebook will pick your header image instead of any images published in your post. Jetpack will give Facebook several options, including any featured image or post thumbnail your post might have and any other images found in your post. Please ensure that your images meet Facebook’s?recommended image dimensions. Also, always clear your site’s cache after making changes, as this can often solve such issues.
Hope that’s all clear! Let me know how you get on.