ubuntu 17.10 server. Bridge not starting on reboot

All of the Ethernet cards start, but the bridge does not. running netplan apply brings up the bridge. How do I make sure the bridge comes up on reboot?

Everything is fine after the netplan apply, but not after reboot. How can I fix this?

contens of .yaml file
network:
   version: 2
   renderer: networkd
   ethernets:
       enp4s0:
           dhcp4: false
           addresses: [192.168.1.15/24]
           gateway4: 192.168.1.1
            nameservers:
                 addresses: [192.168.1.95 192.168.1.244]
       enx0050b60dec7f:
              dhcp4: false
   bridges:
       br0:
           dhcp4: yes
           interfaces: [enx0050b60dec7f]