Website is slow: open_basedir restriction in effect. File is not within the allowed path(s)

Symptoms

Website is slow. The following is logged to /var/www/vhosts/system/example.com/logs/error_log: 

CONFIG_TEXT: [fcgid:warn] [pid 100430] [client 203.0.113.2:35696] mod_fcgid: stderr: PHP Warning:  is_file(): open_basedir restriction in effect. File(/media/jui/js/jquery.min.js) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in /var/www/vhosts/example.com/httpdocs/libraries/joomla/filesystem/file.php on line 564, referer: http://www.example.com
[fcgid:warn] [pid 90739] [client 203.0.113.2:52798] mod_fcgid: stderr: PHP Warning:  is_file(): open_basedir restriction in effect. File(/media/com_wrapper/js/iframe-height.min.js) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in /var/www/vhosts/example.com/httpdocs/libraries/joomla/filesystem/file.php on line 564, referer: http://example.com/

The mentioned file paths do not exist on the system:

# ls -la /media/
total 16
drwxr-xr-x  4 root root 4096 Jun 23  2017 .
drwxr-xr-x 24 root root 4096 May  1 05:57 ..
drwxr-xr-x  2 root root 4096 Jun 23  2017 cdrom
lrwxrwxrwx  1 root root    7 Jun 23  2017 floppy -> floppy0
drwxr-xr-x  2 root root 4096 Jun 23  2017 floppy0

Cause

Website code issue: there are referrals to non-existent files.

Resolution

Contact the website developers to review the website code.

Additional information

The other causes of such error are addressed in the articles below:

A website hosted in Plesk is not accessible: open_basedir restriction in effect

WordPress shows 500 Internal Server Error on Windows: open_basedir restriction in effect