It could be that your VPS has IPv6 privacy extensions enabled. This means that your IPv6 address will change every few minutes. For security reasons, this is not supported on our platform.
Here's how to disable privacy extensions:
On Linux:
echo net.ipv6.conf.all.use_tempaddr=0 >> /etc/sysctl.conf sysctl -p
On Windows 2008:
netsh interface ipv6 set global randomizeidentifiers=disabled store=active netsh interface ipv6 set global randomizeidentifiers=disabled store=persistent
On Windows 2012:
netsh interface ipv6 set global randomizeidentifiers=disabled store=active netsh interface ipv6 set global randomizeidentifiers=disabled store=persistent netsh interface ipv6 set privacy state=disabled store=active netsh interface ipv6 set privacy state=disabled store=persistent