WordPress preview post links not working? Sick of unsuccessfully trying different things you’ve found on Google like I was? Pretty much every article I read offered a different solution. Some suggested it was related to a bad theme update, others that is was related to caching, others still pointed the finger at mod rewrite/isapi rewrite rules. Eventually I gave up and just went with a preview post workaround.
WordPress preview post not working workaround
Well a quick workaround for you might be to just go ahead and publish the post but set its visibility to private. Private content is only visible when you are logged in so can be used to preview posts before publishing to everyone. Note however other editors and administrators will be able to see this content too when they are logged in, but that may be fine for your case. You can set a post to private from the right hand side of the add/edit post page as shown above.
FYI: this is what the post looked like on the site before I made it public