"Empty Reply From Server" => This occurs when php gets killed due to external actions which it cannot control. For eg: while handling files, using openssl functions, etc.

The possible issue could be php openSSL is not configured properly in this case.

To test this, please upload the attached file to the WP site for which you are facing this issue.

Upload the file attached(_testOpenSSL.php) to root directory of the site.

Access the file through browser, say http://example.com/_testOpenSSL.php

There are two possible outcomes:

Case 1: (blank page) - that means it is giving "Empty Reply From Server" error, php couldn't handle it because of openSSL is not configured correctly. Please contact the host of your WP site and give the test URL.

Case 2: If it prints any content like "PHP openSSL works." or "PHP openSSL not working." - then things are ok. "PHP openSSL not working." in this case, IWP will fall back to non openSSL method.