Sorry for the inconvenience, while trying to investigate the problem, I disabled the Elegant Builder plugin by mistake (because it didn't work the first times to disable the plugins due to the interface being in russian... and when it worked, I forgot to uncheck the Elegant Support plugin). Can you please re-enable it back?
Sorry for taking it a little bit longer, but most of the usual things look fine on your server so it's possible that it's something else more tricky causing it.
Can you also please create a phpinfo.php file on your root folder of your WP installation with this code so I can check your server settings?
Can you also try adding this code at the top of your .htaccess file?
<IfModule mod_substitute.c>
SubstituteMaxLineLength 10M
</IfModule>