Citrix Troubleshooting VDI unregistered issue resolved

Hi sir,,
Recently in our infra we are facing this issue daily basis.
Machines are going to unregistered state randomly.
While issue happening, ping status from ddc to vda is request timed out. No communication happening
Unable to take rdp to the unregisterd machine.
Services in ddc are running.
Vms are hosted in v center, vm is stuck with blue windows login screen. Unable to login through remote console. So we are rebooting the vda.
Post reboot everything good.
There is no event logs generated previous boot of tge machibe. After reboot event logs wre tgere.
What could be other possiblities for the cause