So I figured I'd share what I ran into recently. I was running into surebackup failures over the weekend where veeam wasn't able to run the test scripts, even the built in ones. I had to kill all the processes to stop the surebackup job since stopping the job wouldn't do anything. The only thing that changed between this and last week on the server was a run of windows updates. I plugged all the windows updates into the google™ and found one that looked like it might have caused my issue: KB3139914 which is for the secondary logon service.
So I uninstalled that update and voila! my surebackup jobs ran.
The server in question was on 2012 R2
It seems to only affect surebackup jobs tied to application groups where the credentials for the VM are specified instead of being left the default blank.
If someone at veeam or otherwise could test this out and confirm, we might be able to save a bunch of people some headaches.