I'd say this was invoked by the apps running on it. This VM is used for analytics and reporting, it's got Visual Studio, Power Bi and SQL server running on it. The vendor must've been doing some shit on it.
So, because Veeam reapplied the old snapshot, everything between then and now was lost.
If I keep the old snaphot as current, all the systems have domain trust failure.
I have a backup and there is only a single shared folder on here that will need restored.
Because this site is only 20 Windows computers, and I wanted to stop wasting time after 2 hours, I went brute force.
I disjoined everything from the domain and rejoined them.
With that resolved, I restored the C:\shares folder on the DC from the last Veeam backup.
Site is now working again.
Veeam's replication is now also in the correct state to fall back the replica to the main hyper-v server.
Not fucking touching that tonight.. I R DUN.
Edit: Maybe not the perfectly correct answer, but the answer I went with.