What Causes Servers to Disappear from Hyper-V and How Can I Prevent It?

You should definitely look into your logs; VMs don't just vanish without some sort of record. There's usually something in the logs that can help you figure out what went wrong.

Diving deep into the Hyper-V logs can reveal a lot. Don't skip that step; make sure to check them out!

It sounds like your VMs might have deregistered due to some corruption in the database Hyper-V uses. However, if the volumes are also missing, that's a sign of something more serious happening. It's important to check your logs for any clues.

You should take this seriously. Even if right now it looks like a non-issue, investigating it could prevent more significant problems down the line.

I've had a similar issue where permissions related to Active Directory were to blame. If the VM files were still on the disk or if entire folders are missing, that gives different clues. Are you running a cluster setup or is it standalone?

I've seen this happen a few times—sometimes the VMs won't show in the console, but the virtual disks are still there. Restarting the VM management service usually resolves the issue if you're facing something similar.

Also, what version of Hyper-V are you using? The way your VMs are stored, whether it's on shared or local storage, could impact things too. And just a tip: when discussing issues, be clear about whether 'servers' means 'VMs.' This can help others understand better when providing support.