503 error can view or edit page

I have been updating my website and now I am unable to access a page on the backend of wordpress in order to edit it. When I click edit I am redirected to a preview of my home page. I have tried starting from scratch and recreating the page but just get a Invalid JSON Response Error in WordPress so it wont save it.

The page is https://katewatson.org/work/hiddencoststest/

It is linked to one of the posts

Any help appreciated – it was working fine a day or so ago

 

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