I am having the same issue. 2x Hyper-V 2012 R2. One is a Hyper-V only install, the other is full Datacenter with the hyper-V role installed. Veeam is running on a dedicated VM on the full install version, which has a DAS target for backups.
I cannot kill the job when it sticks. I have to restart the Veeam server VM. I sometimes have to restart a few times before I can start the job manually. Endpoint backups never fail (for remaining physical servers), just the job configured for the host servers. If it passes the "Building VMs list" message (15 seconds or so when it works) it will complete. Veeam is currently working as scheduled less than half the time. Will start a new case but just wanted to add support to this one.