This happend on Proxmox KVM host server when tried to restore Snapshot of an Virtual machine (VM).

bridge 'vmbr*' does not exist
/var/lib/qemu-server/pve-bridge: could not launch network script
Failed: exit code 1

(i had vmbr1)

-->

cat /etc/network/interfaces

auto lo
iface lo inet loopback

auto vmbr0
iface vmbr0 inet static
address 199.204.186.45
netmask 255.255.255.192
network 199.204.186.0
broadcast 199.204.186.63
gateway 199.204.186.62
bridge_ports eth0
bridge_stp off
bridge_fd 0
bridge_maxwait 0

auto eth0
iface eth0 inet manual


Im not sure how to fix it, but maybe try to copy whole vmbr0 section and paste it below as vmbr* or any other which is demanded. And maybe try to tweak IP values of thet newly pastet section. http://jodies.de/ipcalc (ip calculator). And maybe try tremoving "bridge" lines from that pasted section.
May try service networking restart on host node.