Sidebar appears below category content

I have setup a child theme and am trying to setup category pages with unique content. I have installed a plugin to allow HTML in the category descriptions and have placed some code in the category description. It shows up as it should, however, the sidebar does not start until the posts do, pushing it some ways down the page.

I have seen several posts about this issue which mostly say the problem is a missing close div, however, most of these posts are 3+ years old and don’t appear to address my issue. I have run W3 Validator and cannot find an instance of a missing close div.

I have made style changes to the child file, but have not touched the parent theme files aside from installing plug-ins by uploading zip files via the WordPress interface.

Thanks so much in advance for your help!