Can you look on the VDP appliance at the log /usr/local/avamar/var/log/av_boot.rb.log ?
In the entries after the reboot, do you see anything like this (where X.X.X.X is the IP of your VDP appliance) ?:
(0.0) ssh -x -o GSSAPIAuthentication=no root@X.X.X.X 'tar xzf .mapall6422; rm -f .mapall6422'
Connection closed by X.X.X.X
ERROR: command "ssh -x -o GSSAPIAuthentication=no root@X.X.X.X 'tar xzf .mapall6422; rm -f .mapall6422'" failed, return: 65280, exitcode: 255, signal: 0, dumped core: 0
I have seen an issue where the environment had multiple VM's with the same IP address as the VDP appliance and the system was not able to start because of this.