Side bar category issue

Hi, I’m having a very strange issue with my wordpress theme (Matra). On one of the categories the oldest post displays in the sidebar, pushing the standard sidebar content down. This only happens in this category – https://keith-stubbs.com/category/editorial-publishing/ and it’s not specific to the post (i.e. if I change the post category, the nest post in this category displays in the sidebar. I can’t for the life of me figure out what it is, but my coding skills are fairly limited. Any help here would be greatly appreciated.