Because of the older kernel version on VPS. There are a lot of messages error and bugs (eg openvpn init script is broken) related to systemd
session-12687140.scope: Failed to set invocation ID on control group /user.slice/user-0.slice/session-1
2687140.scope, ignoring: Operation not permitted
When do you upgrade your old kernel ?
SMP Thu Mar 22 10:58:36 MSK 2018 x86_64 GNU/Linux ouch !