Debian – Systemd: Redis server wont start when run as a service – too many levels of symbolic links

I have recently ran into the issue from the subject. I have installed Debian 9 as a webserver (with nginx, php7.0-fpm and some other stuff) and I want to use redis with my PHP installation. When installing it from the official repos, the package installs fine, but the systemd unit fails to start or enable. When I try to run the command from "ExecStart" from the unit file by hand, redis starts fine and is operational.

Here is the unit file (provided by the Debian package, I have made no modifications):

[Unit]
Description=Advanced key-value store
After=network.target
Documentation=http://redis.io/documentation, man:redis-server(1)

[Service]
Type=forking
ExecStart=/usr/bin/redis-server /etc/redis/redis.conf
PIDFile=/var/run/redis/redis-server.pid
TimeoutStopSec=0
User=redis
Group=redis
RunTimeDirectory=redis

ExecStartPre=-/bin/run-parts --verbose /etc/redis/redis-server.pre-up.d
ExecStartPost=-/bin/run-parts --verbose /etc/redis/redis-server.post-up.d
ExecStop=-/bin/run-parts --verbose /etc/redis/redis-server.pre-down.d
ExecStop=/bin/kill -s TERM $MAINPID
ExecStopPost=-/bin/run-parts --verbose /etc/redis/redis-server.post-down.d

UMask=007
PrivateTmp=yes
LimitNOFILE=65535
PrivateDevices=yes
ProtectHome=yes
ReadOnlyDirectories=/
ReadWriteDirectories=-/var/lib/redis
ReadWriteDirectories=-/var/log/redis
ReadWriteDirectories=-/var/run/redis
CapabilityBoundingSet=~CAP_SYS_PTRACE

# redis-server writes its own config file when in cluster mode so we allow
# writing there (NB. ProtectSystem=true over ProtectSystem=full)
ProtectSystem=true
ReadWriteDirectories=-/etc/redis

[Install]
WantedBy=multi-user.target
Alias=redis.service

Here is the output from journalctl -xe after running "systemctl start redis":

-- Subject: Unit redis-server.service has begun start-up
-- Defined-By: systemd
-- Support: https://www.debian.org/support
-- 
-- Unit redis-server.service has begun starting up.
Aug 16 10:39:05 hathor systemd[9337]: redis-server.service: Failed at step NAMESPACE spawning /bin/run-parts: Too many levels of symbolic links
-- Subject: Process /bin/run-parts could not be executed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
-- 
-- The process /bin/run-parts could not be executed and failed.
-- 
-- The error number returned by this process is 40.
Aug 16 10:39:05 hathor systemd[9340]: redis-server.service: Failed at step NAMESPACE spawning /usr/bin/redis-server: Too many levels of symbolic links
-- Subject: Process /usr/bin/redis-server could not be executed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
-- 
-- The process /usr/bin/redis-server could not be executed and failed.
-- 
-- The error number returned by this process is 40.
Aug 16 10:39:05 hathor systemd[1]: redis-server.service: Control process exited, code=exited status=226
Aug 16 10:39:05 hathor systemd[1]: Failed to start Advanced key-value store.
-- Subject: Unit redis-server.service has failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
-- 
-- Unit redis-server.service has failed.
-- 
-- The result is failed.
Aug 16 10:39:05 hathor systemd[1]: redis-server.service: Unit entered failed state.
Aug 16 10:39:05 hathor systemd[1]: redis-server.service: Failed with result 'exit-code'.

And here is the error message that "systemctl enable redis" gives, wich is the most cryptic to me:

root /lib/systemd/system $ systemctl enable redis
Failed to enable unit: Refusing to operate on linked unit file redis.service

root /lib/systemd/system $ systemctl enable redis-server
Synchronizing state of redis-server.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable redis-server

The unit file is not a symlink, it is a regular file:

-rw-r--r--  1 root root 1.2K Aug 16 10:32 redis-server.service

No points in /etc/, /var/run are symlinks or mountpoins. Only one mount in /mnt/backup exist on this server. I should also mention that this server is a VPS on a OpenVZ host. Systemd version is 232, Debian is fully upgraded to the newest version of packages with kernel 3.16.6-042stab123.8.

Thanks in advance for any advice!
Cheers, Johny