Just found this solution on Quora—worked for me!
https://www.quora.com/How-do-I-get-a-Squarespace-based-site-to-properly-display-its-preview-image-in-LinkedIn-I-have-updated-the-social-media-image-and-site-image-and-it-still-doesnt-come-through-even-though-it-works-fine-on-Facebook