Missing Photo Thumbnail on Older Posts

I have a wedding photo blog. WordPress with Graph Paper Press. The top (most recent) post will show all the photos, then the older ones underneath are compressed to the title with a single thumbnail. Until now. I have done nothing different nor have I updated anything recently. On the “One year shoot” you’ll see the thumbnail – that’s what I want! But the others above it – it is title with no thumbnail. I have no idea what this is suddenly happening. blog is here to see:

https://www.rojopicturesblog.com

thanks.