VR DHCP issue

[Alessandro Caviglione]

Hi guys,
I'm experiencing an issue in our CS 4.9.
In fact, sonce a week ago, randomly some instances became unreachable.
After investigation we see that instances does not have IP address.
We tried to restart VR, restart instance, migrate both to another host, but
same issue.
So we configured the instance with a fixed ip address and it comes back
online.
We have had this issue on about 15 VR...
Any idea??