3rd lvl Nested URLs are 404

Where I should look to fix the issue?

domain.com/url1/url2/url3 – 404
when
domain.com/url1/url2/ - 200

I'm using hosting with litespeed server.
To build nested URLs using "Add Hierarchy (parent) to post" plugin.

are you sure that you mean domain.com/url1/url2/url3 instead of domain.com/slug1/slug2/slug3 ?? Because I've never heard of such a configuration before...

Still, the problem is obviously with the /slug3 part of the page / post / whatever the hell the plugin creates, so you should check the page / post that ends in /slug3, or check the settings of that plugin, or its output (the slugs that it creates).