I’ve done some further testing and it looks like there’s also an issue when the page is saved as a draft.
Basically hitting preview whilst the page is a draft is borked. I have to hit ‘save draft’ and then preview to see the changes. It is completely unworkable to have to publish a page first as I’m using flexible content fields as a page builder.
I’ve tried the work-around in the post but it dates back to 2013 and doesn’t seem to be working.
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