Can not restart services using systemctl on debian-based VM

[SPQRInc]

Hello,

I would like to solve a problem: My KVM- and debian-based VPS refuses to start services after it worked a while without problems.

The restart task hangs at:

root@server:/home/me# /etc/init.d/postfix restart
[....] Restarting postfix (via systemctl): postfix.service

for hours.

Logs are showing

systemd[1]: Looping too fast. Throttling execution a little

Now I would like to solve the problem but I do not know if it is something proxmox-related or a debian-problem.

Any help is appreciated.