/var/run/vservers/$vserver keeps disappearing

Hello,

a short time after my vservers were started, the vserver utility says 
that the vservers are not running anymore. I now discovered that this is 
because /var/run/vservers/$vserver disappear after a short vserver 
uptime. So, I restored the files manually, but they disappeared again. 
What is happening there?

I applied the vserver patch on Debian kernel 4.9.0-6, which really is 
4.9.82 with some patches. util-vserver is version 0.30.216-pre3131.


Regards
    Christoph