Troubleshoot and fix issues with wordpress plugin and theme

I would like a wordpress expert to work on the issues identified below for [login to view URL] We have checked your server once more and collected information that could be helpful to you in resolving this issue. This is what the server error log was showing initially, when the website was getting a 504 error: [Tue Oct 09 11:07:59 2018] [warn] [client ] mod_fcgid: stderr: PHP Warning: include_once(lib/[login to view URL]): failed to open stream: No such file or directory in /var/www/vhosts/[login to view URL] on line 21 [Tue Oct 09 11:07:59 2018] [warn] [client ] mod_fcgid: stderr: PHP Warning: include_once(): Failed opening 'lib/[login to view URL]' for inclusion (include_path='.:/opt/plesk/php/5.6/share/pear') in /var/www/vhosts/[login to view URL] on line 21 And you can see in attached screenshot named Before which error we received. After disabling this WP plugin web page managed to load as you can see in attached screenshot called After but there was no content displayed and following entries appeared in error log [Tue Oct 09 11:14:42 2018] [warn] [client ] mod_fcgid: stderr: PHP Fatal error: Call to undefined function masterslider() in /var/www/vhosts/[login to view URL] on line 1 [Tue Oct 09 11:14:44 2018] [warn] [client ] mod_fcgid: stderr: PHP Fatal error: Call to undefined function masterslider() in /var/www/vhosts/[login to view URL] on line 1, referer: [login to view URL] From the above I suspect that this is caused by plugin called masterslider and theme called storeup.