I have probably same problem in juno:

(here is url, I can't post it becouse my carma is low) ${ack-openstack-domain} / question/11920/router-interfaces-down/

But I have different infrastructure. I have dedicated network node.

  [root@nethost ~]# ovs-ofctl show br-int
OFPT_FEATURES_REPLY (xid=0x2): dpid:00006282de3ad749
n_tables:254, n_buffers:256
capabilities: FLOW_STATS TABLE_STATS PORT_STATS QUEUE_STATS ARP_MATCH_IP
actions: OUTPUT SET_VLAN_VID SET_VLAN_PCP STRIP_VLAN SET_DL_SRC SET_DL_DST SET_NW_SRC SET_NW_DST SET_NW_TOS SET_TP_SRC SET_TP_DST ENQUEUE
 3(int-br-vlan): addr:5a:8a:ac:4d:6a:41
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 4(int-br-ex): addr:36:a4:18:b8:59:7d
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 20204(tap270c51fa-76): addr:62:82:de:3a:d7:49
     config:     PORT_DOWN
     state:      LINK_DOWN
     speed: 0 Mbps now, 0 Mbps max
 20205(qr-1a0e7fd7-63): addr:00:00:00:00:00:00
     config:     PORT_DOWN
     state:      LINK_DOWN
     speed: 0 Mbps now, 0 Mbps max
 20206(qg-8d652de9-58): addr:62:82:de:3a:d7:49
     config:     PORT_DOWN
     state:      LINK_DOWN
     speed: 0 Mbps now, 0 Mbps max
 LOCAL(br-int): addr:62:82:de:3a:d7:49
     config:     PORT_DOWN
     state:      LINK_DOWN
     speed: 0 Mbps now, 0 Mbps max
OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0

But in the compute node this problem is not:

root@study-node1 ~]# ovs-ofctl show br-int
OFPT_FEATURES_REPLY (xid=0x2): dpid:0000921686a17848
n_tables:254, n_buffers:256
capabilities: FLOW_STATS TABLE_STATS PORT_STATS QUEUE_STATS ARP_MATCH_IP
actions: OUTPUT SET_VLAN_VID SET_VLAN_PCP STRIP_VLAN SET_DL_SRC SET_DL_DST SET_NW_SRC SET_NW_DST SET_NW_TOS SET_TP_SRC SET_TP_DST ENQUEUE
 1(int-br-vlan): addr:b6:9e:98:e2:31:e4
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 2(int-br-ex): addr:1a:5a:dc:82:75:c4
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 5(qvoab4d8929-f4): addr:be:f4:19:e3:10:01
     config:     0
     state:      0
     current:    10GB-FD COPPER
     speed: 10000 Mbps now, 0 Mbps max
 6(qvo0299a927-ae): addr:76:d2:b4:bf:f3:a4
     config:     0
     state:      0
     current:    10GB-FD COPPER
     speed: 10000 Mbps now, 0 Mbps max
 LOCAL(br-int): addr:92:16:86:a1:78:48
     config:     PORT_DOWN
     state:      LINK_DOWN
     speed: 0 Mbps now, 0 Mbps max
OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0

And pings between VMs work, but it can't get the IP by dhcp. It is namespaces in network node:

[root@nethost ~]# ip netns 
qrouter-7573b61c-1cb2-43bc-8296-421e319d2bd0
qdhcp-f8bdf250-d08f-467a-a073-003ea3165c5d
[root@nethost ~]#

The ping is works from root namespace to router, but from root to dhcp is not:

[root@nethost ~]# ip netns exec qrouter-7573b61c-1cb2-43bc-8296-421e319d2bd0 ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

qg-8d652de9-58: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.2.57.68  netmask 255.255.255.0  broadcast 10.2.57.255
        inet6 fe80::f816:3eff:fe4e:b045  prefixlen 64  scopeid 0x20 ...