forum_post_thread_chooser is displaying in columns

[Ferdinand]

I'm not sure where I have lost this but the whole site is displaying at full width but when I load the page /forums/-/post-thread

It's divided in to columns. I'd like it to be full page width while the site remains responsive as it always has been. Any ideas what's going wrong here:

URL: https://atomicacademia.com/forums/-/post-thread

The template isn;t edited.
forum_post_thread_chooser is displaying in columns

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