Posts show up but cannot see the whole articles — custom ‘add post’ form

I created a sample form for adding new posts available for everyone as a wordpress page. It’s simple and specialized — it’s not important why I need it for the question.

So, the thing is — when I add new posts using this form, everything works, tha post is added to a category, it shows up on my main page, etc, but when I click on the title, the whole content does not appear! I checked the generated stub — it looks reasonable. I checked in the wp_posts table — the post data looks exactly as other posts’ data (which show up normally).

Now, what can be the reason for that? I suspect the rewrite rules in some way, but no idea where to go with that…