I’m seeing the same issue on my side. Ben has already identified the cause. It seems to be related to different types of quotes being used in the Markdown frontmatter.
At least that was the case for me. Unfortunately, it’s not very easy to spot the difference between normal quotes and smart quotes in the Elements Markdown editor.
I had ChatGPT replace all the quotes in my Markdown files with normal ones, and everything is working again now. I assume there will probably be an update for this later today — or you can do what I did and have everything corrected.