I have two lxc on the same node, one networking normal and the other networking wrong.
# cat /etc/pve/lxc/103.conf
...
net0: name=eth0,bridge=vmbr1,firewall=1,gw=192.168.10.254,hwaddr=0E:BB:3B:B6:A4:E6,ip=192.168.10.70/24,tag=300,type=veth
...
# cat /etc/pve/lxc/202.conf
...
net0...