Thanks for reaching out.
I appreciate the context that you have shared, can you let us know where the store link is being shared? If you are attempting to share the store link on Facebook, it may take a number of days before Facebook checks for updates.
With that being said, I would suggest confirming that you saved the image within the Social sharing image section within the Preferences. I took a screenshot from my test store to show you the sections I am referring to:
If you can confirm that the image is added and saved, we can preview what your social image may look like on some platforms with tools like Twitter's Card Validator, Facebook's Crawler and LinkedIn's Post Inspector.
Looking forward to your reply.
You should upload an image of best size 1200px x 630px width-to-height. The format is jpg, png. Just upload the compatible image and scrape the page link with facebook debugger.
Usually, it's due to cache, image format or size issue