Website fails to load due to internal redirects: 500 Internal Server Error

Symptoms

• The website fails to load with error:

  external Server Error
  The server encountered an internal error or misconfiguration and was unable to complete your request.
  Please contact the server administrator, info@example.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
  More information about this error may be available in the server error log.

• /var/www/vhosts/system/example.com/logs/error_log
contains the following:

  [error] [client 203.0.113.2] Request exceeded the limit of 10 external redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace., referer: http://example.com/

  OR

  [core:alert] [pid 18159] [client 203.0.113.2:38306] /var/www/vhosts/example.com/httpdocs/.htaccess: without matching section

  OR

  [core:alert] /var/www/vhosts/example.com/httpdocs/.htaccess: Invalid command 'alllow', perhaps misspelled or defined by a module not included in the server configuration Apache error

  OR

  [proxy_fcgi:error] [pid 6378:tid 140153632777984] [client 203.0.113.2:57368] malformed header from script 'index.php': Bad header

Cause

Incorrect rewrite rules in
.htaccess
file causing constant redirecting.

Resolution

1. Log into Plesk;
2. Navigate to Domains > example.com > File Manager;
3. Rename the .htaccess:
   

   or replace .htaccess content with default one by slelcting Edit... option on the above sceen:

   # BEGIN WordPress
   RewriteEngine On
   RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
   RewriteBase /
   RewriteRule ^index.php$ - [L]
   RewriteCond %{REQUEST_FILENAME} !-f
   RewriteCond %{REQUEST_FILENAME} !-d
   RewriteRule . /index.php [L]

Note: If
.htaccess
file is not present on any level of
httpdocs
directory, consider checking subscription directory, e.g.
/var/www/vhosts/example.com