I'm not sure if anyone can help with this, but I'm fairly sure it's not a theme issue or the fault of the toggle plugin, but for some reason, the 'toggle' shortcode doesn't work in some categories. I'm using this plugin:
However, I've tried other toggle plugins and had the same issue.
You can see here that it doesn't work:
but here it does:
https://www.simfansuk.com/wp/ancient-rome-colosseum/ (click the 'Details' tab)
I've tried lots of themes, and it's the same with all of them. I've tried disabling all of the plugins except the toggle one, and it still happens. I'm beginning to think it's a problem with Wordpress itself, but I'm a programming dunce so have no idea how to troubleshoot!