I kept on searching, and finally found something that fixed this issue.
For those who are using CentOs 7 in combination with Plesk 12:
The issue is with SELinux.
When it’s used in Enforcing mode (which is the default),
wp-content
does not show itself via FTP. Switching it to Permissive mode or
disabling SELinux altogether solves the problem.The entire issue will be fixed in the next release of Plesk, and it’s
already working in the latest update to the Plesk Preview 12.1.13.
CentOS 5 and 6 are not affected.
To disable SELinux on CentOS 7 we can use this: setenforce 0
Or, to switch to permissive mode, use this: setenforce permissive
Now we’ll need to restart the xinetd service as well as Plesk for the changes to take effect:
systemctl restart xinetd.service
service psa stopall
service psa restart
If the server is restarted the above settings will be lost.
To permanently use the above settings you should edit the selinux config file:
vi /etc/selinux/config
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
SELINUX=enforcing
# SELINUXTYPE= can take one of these two values:
# targeted - Targeted processes are protected,
# minimum - Modification of targeted policy. Only selected processes are protected.
# mls - Multi Level Security protection.
SELINUXTYPE=targeted