No thumbnail or title for projects shared to social media (branched to separate thread)

I am having is that when I share the project on social media (i.e. Facebook), a thumbnail showing my first image of the project along with the title no longer gets generated.  All I get is a boring gray background with the words "EXPRESS.ADOBE.COM" on it.  I tried everything I could think of to generate a thumbnail like Adobe Spark used to produce, but it just will not work.  Without such a thumbnail, little (if any) attention gets drawn to my posts.  As a comparison, the last time I produced a project using Adobe Spark and with the thumbnail generated, I had over 100 likes; this time, with only a gray background and some text, I've only had 5.  I placed a post about this on this forum but no one has replied.  Are you able to help?  Thanks again for your assistance.