Pages Not Working On Child Theme

Hello

I’ve been running a child theme on my blog for a couple of years without a problem https://rdldn.co.uk/

However, a couple of weeks ago, it stopped working – without any action from myself.

Specifically the issue is that pages such as https://rdldn.co.uk/league-of-roasts/ just show the homepage.

All posts work fine.

I have tried a variety of ways to fix this, including a full rebuild on a different child theme – the problem still happens.

I have tried using WP_DEBUG but no error messages display.

I can change the permalinks to something unhelpful, such as plain, and the page shows correctly. However when I change back to what I want – post-name, it then no longer works.

I also have the same issue on my local dev environment, running a WordPress 4.7 as opposed to the latest version on live.

Does anyone have any ideas?

Kind regards
James

The page I need help with: [log in to see the link]