How to fix 500 Internal Server Error when logging into the Bitrix admin panel after transferring from test to production?

Question

1C-Bitrix

when transferring from a test hosting to a production hosting, when we go to the link http://site_name/bitrix/admin/ or http://site_name/bitrix/admin/index.php... it gives 500 Internal Server Error
, if you enter http://site_name/bitrix/admin/gfdggfdg, then it already enters, issues 404 in the admin panel itself and you can already navigate and work in it. Any ideas what's wrong, where to dig and how to fix it?
The hosting TP said that she had no ideas for solving the problem.
Apache log related to this issue:
[Tue Oct 08 16:57:32.512957 2019] [core:error] [pid 2283] [client 95.79.108.23:64931] End of script output before headers: index.php, referer: http://site_name/bitrix/admin/
.htaccess file code:

Options -Indexes 
ErrorDocument 404 /404.php

<IfModule mod_php5.c>
  php_flag session.use_trans_sid off
  #php_flag default_charset UTF-8
  #php_value display_errors 1
</IfModule>

<IfModule mod_php7.c>
  php_flag session.use_trans_sid off
  #php_flag default_charset UTF-8
  #php_value display_errors 1
</IfModule>

<IfModule mod_rewrite.c>
  Options +FollowSymLinks
  RewriteEngine On
      
  # ASPRO_ROBOTS Serve robots.txt with robots.php only if the latter exists
  RewriteCond %{REQUEST_FILENAME} robots.txt
  RewriteCond %{DOCUMENT_ROOT}/robots.php -f
  RewriteRule ^(.*)$ /robots.php [L]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-l
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !/bitrix/urlrewrite.php$
  RewriteRule ^(.*)$ /bitrix/urlrewrite.php [L]
  RewriteRule .* - [E=REMOTE_USER:%{HTTP:Authorization}]
</IfModule>

<IfModule mod_dir.c>
  DirectoryIndex index.php index.html
</IfModule>

<IfModule mod_expires.c>
  ExpiresActive on
  ExpiresByType image/jpeg "access plus 3 day"
  ExpiresByType image/gif "access plus 3 day"
  ExpiresByType image/png "access plus 3 day"
  ExpiresByType text/css "access plus 3 day"
  ExpiresByType application/javascript "access plus 3 day"  
</IfModule>

Answer 1

You would show Apache logs.
Well, there is a suspicion that you should not connect both php5 and php7 at the same time

Answer 2

See logs.
Try disabling everything in Settings -> Proactive Defense before migrating.
Be sure to add all domains to hosts/domains Most of the
time my website copies don't work when I forget to add them there

Answer 3

contacting Bitrix without understanding where to look for Apache logs and what to look in them - you are, of course, a very brave person.