@Yaroslav_Bulatov I had this happen to me last year and so reported it as a bug over on GitHub. It was closed though due to it not being reproducible by Ghost staff and due to me apparently being too lazy to take it any further. Here’s the issue I raised:
I meant to suggest that the browser might be caching the 404 error or something.
I have a Ghost instance installed on DO and I don’t see 404 when I open the preview link. And I’m signed into the admin as well.
But the caching issue happens to me all the time, especially when I reconfigure domains.
When I reconfigured my domain to point to DO, the normal browser window wouldn’t show my site. Then I checked it via incognito and it worked, which meant that even though the domain had already propagated, the normal browser window was caching the state of my website before propagation.
It’s just a thought.
But if you can replicate the issue in incognito, then it’s not a caching issue.