Incorrect image displayed when post is shared on social media... need help.

Previously when I would write a new blog post, I would go into the SEO settings and change the picture that would display with the post when it was shared on social media. But, now there seems to be an error in that function. For the current post I am finishing, I have changed the image that should display when the post is shared on social media. In the SEO settings preview box, I can see the correct image displayed. However, when I publish the post and click to share it on social media, the image displayed is just a cropped version of the first image in the actual blog post rather than the image I had selected for display in social media shares. I have been trying to fix the issue for two days to no avail. I have not had this problem before with any of my other posts. What do I need to do to resolve this issue?