Page shows on the site, but registers as a 404 error

it is 404 for me too.

Is the page published with public access?

Yes. I’ve turned off WP-Rocket, which has caching, purged the browser cache on my computer and can still see it, but if you can’t see it, that implies it is a caching problem. I guess what I’m seeing is nothing to do with WordPress and everything to do with caches not purging properly.

Make sure, you don’t have a page and post with the same slug.

If that is not the case then try this
In your backend go to Settings > Permalink page, Then if you’re using Custom Structure then copy the structure from input and paste it into a notepad for backup.

Then choose the Plain option in permalink settings and save the settings.
Then go to your pages or posts and find that page/post that you have a problem with and click on view, it should be accessible with this kind of URL https://example.com/?p=12345

if it’s accessible then got back to permalink and set the old permalink and save then check if it’s come back.

I have to admit I was scared about messing with permalink. But this was helpful in a roundabout way. What I suspected in the earlier post was that, somehow, the cache wasn’t clearing out the page, changing the permalink to a p number and then finding the page really was missing after all meant I solved the issue.

Glad to know, you solved it.