How to fix 404 Not Found Joomla 3?

Question

Joomla

The site runs on Joomla CMS 3.8.2
When you click on a link with the site.ru/page1 format , an error 404 occurs.
If you set the settings as in the screenshot, then all links work adequately on the site, the name is not quite the desired type site.ru/index. php/page
PS Before there was a cyclic https-http redirect when installing SSL, I solved the problem by editing the uri.php file. I am attaching the source and the modified file to the post. The location changed in the file is marked in bold. Thank you!
original

<?php
/**
 * Joomla! Content Management System
 *
 * @copyright  Copyright (C) 2005 - 2018 Open Source Matters, Inc. All rights reserved.
 * @license    GNU General Public License version 2 or later; see LICENSE.txt
 */

namespace Joomla\CMS\Uri;

defined('JPATH_PLATFORM') or die;

/**
 * JUri Class
 *
 * This class serves two purposes. First it parses a URI and provides a common interface
 * for the Joomla Platform to access and manipulate a URI.  Second it obtains the URI of
 * the current executing script from the server regardless of server.
 *
 * @since  1.7.0
 */
class Uri extends \Joomla\Uri\Uri
{
  /**
   * @var    Uri[]  An array of JUri instances.
   * @since  1.7.0
   */
  protected static $instances = array();

  /**
   * @var    array  The current calculated base url segments.
   * @since  1.7.0
   */
  protected static $base = array();

  /**
   * @var    array  The current calculated root url segments.
   * @since  1.7.0
   */
  protected static $root = array();

  /**
   * @var    string  The current url.
   * @since  1.7.0
   */
  protected static $current;

  /**
   * Returns the global JUri object, only creating it if it doesn't already exist.
   *
   * @param   string  $uri  The URI to parse.  [optional: if null uses script URI]
   *
   * @return  Uri  The URI object.
   *
   * @since   1.7.0
   */
  public static function getInstance($uri = 'SERVER')
  {
    if (empty(static::$instances[$uri]))
    {
      // Are we obtaining the URI from the server?
      if ($uri == 'SERVER')
      {
        // Determine if the request was over SSL (HTTPS).
        if (isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https')
        {
          $https = 's://';
        }
        elseif ((isset($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
          !empty($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
          (strtolower($_SERVER['HTTP_X_FORWARDED_PROTO']) !== 'http')))
        {
          $https = 's://';
        }
        else
        {
          $https = '://';
        }

        /*
         * Since we are assigning the URI from the server variables, we first need
         * to determine if we are running on apache or IIS.  If PHP_SELF and REQUEST_URI
         * are present, we will assume we are running on apache.
         */

        if (!empty($_SERVER['PHP_SELF']) && !empty($_SERVER['REQUEST_URI']))
        {
          // To build the entire URI we need to prepend the protocol, and the http host
          // to the URI string.
          $theURI = 'http' . $https . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
        }
        else
        {
          /*
           * Since we do not have REQUEST_URI to work with, we will assume we are
           * running on IIS and will therefore need to work some magic with the SCRIPT_NAME and
           * QUERY_STRING environment variables.
           *
           * IIS uses the SCRIPT_NAME variable instead of a REQUEST_URI variable... thanks, MS
           */
          $theURI = 'http' . $https . $_SERVER['HTTP_HOST'] . $_SERVER['SCRIPT_NAME'];

          // If the query string exists append it to the URI string
          if (isset($_SERVER['QUERY_STRING']) && !empty($_SERVER['QUERY_STRING']))
          {
            $theURI .= '?' . $_SERVER['QUERY_STRING'];
          }
        }

        // Extra cleanup to remove invalid chars in the URL to prevent injections through the Host header
        $theURI = str_replace(array("'", '"', '<', '>'), array('%27', '%22', '%3C', '%3E'), $theURI);
      }
      else
      {
        // We were given a URI
        $theURI = $uri;
      }

      static::$instances[$uri] = new static($theURI);
    }

    return static::$instances[$uri];
  }

  /**
   * Returns the base URI for the request.
   *
   * @param   boolean  $pathonly  If false, prepend the scheme, host and port information. Default is false.
   *
   * @return  string  The base URI string
   *
   * @since   1.7.0
   */
  public static function base($pathonly = false)
  {
    // Get the base request path.
    if (empty(static::$base))
    {
      $config = \JFactory::getConfig();
      $uri = static::getInstance();
      $live_site = ($uri->isSsl()) ? str_replace('http://', 'https://', $config->get('live_site')) : $config->get('live_site');

      if (trim($live_site) != '')
      {
        $uri = static::getInstance($live_site);
        static::$base['prefix'] = $uri->toString(array('scheme', 'host', 'port'));
        static::$base['path'] = rtrim($uri->toString(array('path')), '/\\');

        if (defined('JPATH_BASE') && defined('JPATH_ADMINISTRATOR'))
        {
          if (JPATH_BASE == JPATH_ADMINISTRATOR)
          {
            static::$base['path'] .= '/administrator';
          }
        }
      }
      else
      {
        static::$base['prefix'] = $uri->toString(array('scheme', 'host', 'port'));

        if (strpos(php_sapi_name(), 'cgi') !== false && !ini_get('cgi.fix_pathinfo') && !empty($_SERVER['REQUEST_URI']))
        {
          // PHP-CGI on Apache with "cgi.fix_pathinfo = 0"

          // We shouldn't have user-supplied PATH_INFO in PHP_SELF in this case
          // because PHP will not work with PATH_INFO at all.
          $script_name = $_SERVER['PHP_SELF'];
        }
        else
        {
          // Others
          $script_name = $_SERVER['SCRIPT_NAME'];
        }

        // Extra cleanup to remove invalid chars in the URL to prevent injections through broken server implementation
        $script_name = str_replace(array("'", '"', '<', '>'), array('%27', '%22', '%3C', '%3E'), $script_name);

        static::$base['path'] = rtrim(dirname($script_name), '/\\');
      }
    }

    return $pathonly === false ? static::$base['prefix'] . static::$base['path'] . '/' : static::$base['path'];
  }

  /**
   * Returns the root URI for the request.
   *
   * @param   boolean  $pathonly  If false, prepend the scheme, host and port information. Default is false.
   * @param   string   $path      The path
   *
   * @return  string  The root URI string.
   *
   * @since   1.7.0
   */
  public static function root($pathonly = false, $path = null)
  {
    // Get the scheme
    if (empty(static::$root))
    {
      $uri = static::getInstance(static::base());
      static::$root['prefix'] = $uri->toString(array('scheme', 'host', 'port'));
      static::$root['path'] = rtrim($uri->toString(array('path')), '/\\');
    }

    // Get the scheme
    if (isset($path))
    {
      static::$root['path'] = $path;
    }

    return $pathonly === false ? static::$root['prefix'] . static::$root['path'] . '/' : static::$root['path'];
  }

  /**
   * Returns the URL for the request, minus the query.
   *
   * @return  string
   *
   * @since   1.7.0
   */
  public static function current()
  {
    // Get the current URL.
    if (empty(static::$current))
    {
      $uri = static::getInstance();
      static::$current = $uri->toString(array('scheme', 'host', 'port', 'path'));
    }

    return static::$current;
  }

  /**
   * Method to reset class static members for testing and other various issues.
   *
   * @return  void
   *
   * @since   1.7.0
   */
  public static function reset()
  {
    static::$instances = array();
    static::$base = array();
    static::$root = array();
    static::$current = '';
  }

Modified (excerpted snippet):

<?php
/**
 * Joomla! Content Management System
 *
 * @copyright  Copyright (C) 2005 - 2018 Open Source Matters, Inc. All rights reserved.
 * @license    GNU General Public License version 2 or later; see LICENSE.txt
 */

namespace Joomla\CMS\Uri;

defined('JPATH_PLATFORM') or die;

/**
 * JUri Class
 *
 * This class serves two purposes. First it parses a URI and provides a common interface
 * for the Joomla Platform to access and manipulate a URI.  Second it obtains the URI of
 * the current executing script from the server regardless of server.
 *
 * @since  1.7.0
 */
class Uri extends \Joomla\Uri\Uri
{
  /**
   * @var    Uri[]  An array of JUri instances.
   * @since  1.7.0
   */
  protected static $instances = array();

  /**
   * @var    array  The current calculated base url segments.
   * @since  1.7.0
   */
  protected static $base = array();

  /**
   * @var    array  The current calculated root url segments.
   * @since  1.7.0
   */
  protected static $root = array();

  /**
   * @var    string  The current url.
   * @since  1.7.0
   */
  protected static $current;

  /**
   * Returns the global JUri object, only creating it if it doesn't already exist.
   *
   * @param   string  $uri  The URI to parse.  [optional: if null uses script URI]
   *
   * @return  Uri  The URI object.
   *
   * @since   1.7.0
   */
  public static function getInstance($uri = 'SERVER')
  {
    if (empty(static::$instances[$uri]))
    {
      // Are we obtaining the URI from the server?
      if ($uri == 'SERVER')
      {
        <b>// Determine if the request was over SSL (HTTPS).
        if (isset($_SERVER['HTTPS']) && !empty($_SERVER['HTTPS']) && (strtolower($_SERVER['HTTPS']) != 'off'))
        {
          $https = 's://';
        }
        elseif ((isset($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
          !empty($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
          (strtolower($_SERVER['HTTP_X_FORWARDED_PROTO']) !== 'http')))
        {
          $https = 's://';
        }
        else
        {
          $https = 's://';
        }
}<b>

Answer 1

So, ladies and gentlemen, victory!
I think this is an actual problem, so I will try to alleviate the suffering of others.
Here's what we do:
1) Enable SSL in the Joomla settings
2) If you can't log into the panel due to an error, change the configuration.php (located at the root) line public $force_ssl = '2'; to public $force_ssl = '';
3) In /libraries/src/Uri/Uri.php change the last line where $https is like this: $https = 's://'

// Determine if the request was over SSL (HTTPS).
        if (isset($_SERVER['HTTPS']) && !empty($_SERVER['HTTPS']) && (strtolower($_SERVER['HTTPS']) != 'off'))
        {
          $https = '://';
4
        }
        elseif ((isset($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
          !empty($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
          (strtolower($_SERVER['HTTP_X_FORWARDED_PROTO']) !== 'http')))
        {
          $https = 's://';
        }
        else
        {
          $https = '://';
        }

4) After that, download the standard .htaccsess, google it in no time
. Done! Three days of suffering, a ton of forums, but I did it. Through thorns to the stars, comrades.

Answer 2

First, update Joomla, now it's 3.9.12 version.
Secondly, why did you get into the files if everything is perfectly configured in the admin panel? You clumsily translated to https and then got into the files to distort, this is your mistake.