Why is a 404 error not being returned?

Question

htaccess

Situation: WordPress site. I specifically refer to a non-existent resource https://site.ru/proekty/proekty-2/proek or https://site.ru/proekty/pro/ , but the site gives the code 301 and opens https://site.ru/proekty /
https://site.ru/n redirects to https://site.ru/news/.
Every time I check in private browser mode, from another machine, from my phone. The result is the same everywhere. In .htaccess is this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress
AddDefaultCharset utf-8
AddType 'text/html; charset=utf-8' .html .htm .shtml

What to do?

Answer 1

On the official https://wordpress.org/plugins/browse/beta/ (taken from the first available) when accessing https://wordpress.org/plugins/browse/bet leads to https://wordpress.org/plugins/
8 -)
update:
people suggested that this is the result of the behavior of the function described in https://developer.wordpress.org/reference/function...
If you wish, you can find a plugin that disables this behavior.

Answer 2

In .htaccess, what the wordpress settings require.
If you have a "proekty" category, then when you open everything that does not exist at a higher level, there will be a redirect to the category. In general, it is worth looking at the plugins / engine / design settings. Such a redirect may be configured somewhere there.

Answer 3

Check if you have a 404.php file