No sidebar and only one post on category pages

Hi, I am really liking this theme and considering upgrading to the pro version but have a fairly big problem I would like to solve before doing that.

When I click into a category page, the sidebar isn’t showing up, and only one post is displayed. As I want people to be able to search within categories this is a bit of a problem.

I’ve tried using other themes to see if the issue is replicated, but it’s only with this theme.

What’s going on? Here’s a link to one of the category pages I’m talking about: https://www.essexmums.com/pregnancy-and-parenting/category/babies/a-mums-experience-babies/

Thanks