As site owners, we can only control the meta tags and Schema markup offered to social and search sites. How those social and search sites decide to use the information provided in meta tags and Schema markup is up to them. What WPSSO does is make sure the information provided conforms to the requirements of each social and search site, which includes the resolution of each image offered in meta tags and Schema markup.
Since you did not include a URL to an example post/page on your site, I cannot comment on any specific image in your meta tags or Schema markup, but what I can suggest is to make sure there are no image related warnings or errors from WPSSO when saving a post/page. If there are any warnings or errors, especially for missing or under-sized images, then you should take those seriously and implement the suggested fixes.
Also, using the validation tools suggested in the SSO > Setup Guide is always a good idea.
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