Internal Server Error Codeigniter HMVC

I ported the codeigniter project to the server from localhost but ran into an " Internal Server Error (500)" issue . (I zipped the whole project directory and extracted it to the server) What I was trying to fix.

• Hosted index.html file in project root and works fine

• hosted the default .htaccess file, also tried without that.

• I tried to echo / print something in the index.php file but it fails and gives an "Internal Server Error"

• I tried to find error_log and it is empty.

• I changed $config['log_threshold'] = 4;
  
  and tried to find the error_log file in application/log/
  
  but it is empty.

• I checked the mod_rewrite issue on the server and it is fine as well and many other projects run without issue.

I am wondering why this is happening in index.html but not in index.php? What other ways can I find and fix this problem?