It took me hours to find a solution to a problem perhaps similar to yours, in that the homepage meta title and description weren’t showing, whereas all the other pages were okay.
In the left navigation, go to SEO > Titles.
At the top of the page fill in Homepage Title template and Meta description template.
Click the Save button at the bottom of the page and you’re good to go.
At least, I hope that solves your problem 🙂