I get it as you had VAL working on Mint 18, then you've updated the system to Mint 19, performed the backup, and tried to restore the system with Veeam Recovery Media. If so, then:
1. Is it the actual system not functioning, or it is just the desktop environment not working properly?
2. Would you share you disks layout, please?
3. Do you have any specific drivers on your system (nvidia, for example)? If yes, then I bet you had to update the driver as well, hence the question - did you patch the recovery media with that new driver?
The restore that does not bring the machine back to its working state is undesirable, for sure. However, given that the system update got it running, I would say it might be not really related to the agent (provided that the agent hasn't been updated).
Anyway the described behaviour is weird. Should you encounter the same problem again, please collect all logs (agent logs + system logs) before updating.
Another thing to mentioned is that although we are considering adding support for Linux Mint in future, it is not officially supported yet.
Totes my own fault! Have to restore /boot with root. Otherwise dodge results. Was misreading volume layout syntax due to pure stupidity. Bare metal restore! Proper!