I try again, but it reproduce easyily.
log info about dhcp-agent and ovs-vswitchd when restarting ovs service:
[root@controller openvswitch-2.6.1]# tailf /var/log/neutron/dhcp-agent.log
2017-08-11 03:07:16.703 17827 INFO neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: connection closed by peer
2017-08-11 03:07:17.703 17827 INFO neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: connecting...
2017-08-11 03:07:17.704 17827 INFO neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: connected
2017-08-11 03:07:17.706 17827 WARNING neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: send error: Connection refused
2017-08-11 03:07:17.807 17827 WARNING neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: connection dropped (Connection refused)
2017-08-11 03:07:17.807 17827 INFO neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: waiting 2 seconds before reconnect
2017-08-11 03:07:19.807 17827 INFO neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: connecting...
2017-08-11 03:07:19.808 17827 INFO neutron.agent.ovsdb.native.vlog [-] tcp:127.0.0.1:6640: connected

[root@controller ~]# tailf /var/log/openvswitch/ovs-vswitchd.log
2017-08-11T07:07:15.487Z|00320|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: connection closed by peer
2017-08-11T07:07:15.487Z|00321|rconn|INFO|br-int<->tcp:127.0.0.1:6633: connection closed by peer
2017-08-11T07:07:15.487Z|00322|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: connection closed by peer
2017-08-11T07:07:17.632Z|00001|vlog|INFO|opened log file /var/log/openvswitch/ovs-vswitchd.log
2017-08-11T07:07:17.636Z|00002|ovs_numa|INFO|Discovered 12 CPU cores on NUMA node 0
2017-08-11T07:07:17.636Z|00003|ovs_numa|INFO|Discovered 12 CPU cores on NUMA node 1
2017-08-11T07:07:17.636Z|00004|ovs_numa|INFO|Discovered 2 NUMA nodes and 24 CPU cores
2017-08-11T07:07:17.636Z|00005|reconnect|INFO|unix:/var/run/openvswitch/db.sock: connecting...
2017-08-11T07:07:17.636Z|00006|reconnect|INFO|unix:/var/run/openvswitch/db.sock: connected
2017-08-11T07:07:17.640Z|00007|dpdk|ERR|DPDK not supported in this copy of Open vSwitch.
2017-08-11T07:07:17.646Z|00008|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports recirculation
2017-08-11T07:07:17.646Z|00009|ofproto_dpif|INFO|netdev@ovs-netdev: MPLS label stack length probed as 3
2017-08-11T07:07:17.646Z|00010|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports truncate action
2017-08-11T07:07:17.646Z|00011|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports unique flow ids
2017-08-11T07:07:17.646Z|00012|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports ct_state
2017-08-11T07:07:17.646Z|00013|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports ct_zone
2017-08-11T07:07:17.646Z|00014|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports ct_mark
2017-08-11T07:07:17.646Z|00015|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath supports ct_label
2017-08-11T07:07:17.646Z|00016|ofproto_dpif|INFO|netdev@ovs-netdev: Datapath does not support ct_state_nat
2017-08-11T07:07:17.725Z|00017|bridge|INFO|bridge br-int: added interface qg-1c51a194-ca on port 4
2017-08-11T07:07:17.725Z|00018|bridge|INFO|bridge br-int: added interface int-br-vlan on port 5
2017-08-11T07:07:17.725Z|00019|bridge|INFO|bridge br-int: added interface tap2588e337-5f on port 2
2017-08-11T07:07:17.726Z|00020|bridge|INFO|bridge br-int: added interface br-int on port 65534
2017-08-11T07:07:17.726Z|00021|bridge|INFO|bridge br-int: added interface int-br-flat on port 9
2017-08-11T07:07:17.726Z|00022|bridge|INFO|bridge br-int: added interface tap26b12348-90 on port 7
2017-08-11T07:07:17.726Z|00023|bridge|INFO|bridge br-int: added interface int-br-ex on port 6
2017-08-11T07:07:17.726Z|00024|bridge|INFO|bridge br-vlan: added interface enp3s0f0 on port 1
2017-08-11T07:07:17.726Z|00025|bridge|INFO|bridge br-vlan: added interface br-vlan on port 65534
2017-08-11T07:07:17.727Z|00026|bridge|INFO|bridge br-vlan: added interface phy-br-vlan on port 2
2017-08-11T07:07:17.727Z|00027|bridge|INFO|bridge br-ex: added interface br-ex on port 65534
2017-08-11T07:07:17.727Z|00028|bridge|INFO|bridge br-ex: added interface phy-br-ex on port 1
2017-08-11T07:07:17.727Z|00029|bridge|INFO|bridge br-int: using datapath ID 000066dc70646340
2017-08-11T07:07:17.727Z|00030|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:17.727Z|00031|connmgr|INFO|br-int: added service controller "punix://var/run/openvswitch/br-int.mgmt"
2017-08-11T07:07:17.727Z|00032|connmgr|INFO|br-int: added primary controller "tcp:127.0.0.1:6633"
2017-08-11T07:07:17.727Z|00033|rconn|INFO|br-int<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:17.727Z|00034|rconn|WARN|br-int<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:17.727Z|00035|rconn|INFO|br-int<->tcp:127.0.0.1:6633: waiting 1 seconds before reconnect
2017-08-11T07:07:17.809Z|00036|bridge|INFO|bridge br-vlan: using datapath ID 00003cfdfe0975c0
2017-08-11T07:07:17.809Z|00037|connmgr|INFO|br-vlan: added service controller "punix://var/run/openvswitch/br-vlan.mgmt"
2017-08-11T07:07:17.810Z|00038|connmgr|INFO|br-vlan: added primary controller "tcp:127.0.0.1:6633"
2017-08-11T07:07:17.810Z|00039|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:17.810Z|00040|rconn|WARN|br-vlan<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:17.810Z|00041|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: waiting 1 seconds before reconnect
2017-08-11T07:07:17.892Z|00042|bridge|INFO|bridge br-ex: using datapath ID 0000e246341f2d4a
2017-08-11T07:07:17.892Z|00043|connmgr|INFO|br-ex: added service controller "punix://var/run/openvswitch/br-ex.mgmt"
2017-08-11T07:07:17.892Z|00044|connmgr|INFO|br-ex: added primary controller "tcp:127.0.0.1:6633"
2017-08-11T07:07:17.892Z|00045|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:17.892Z|00046|rconn|WARN|br-ex<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:17.892Z|00047|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: waiting 1 seconds before reconnect
2017-08-11T07:07:17.972Z|00048|ovs_numa|WARN|Invalid cpu mask: x
2017-08-11T07:07:17.975Z|00049|rconn|INFO|br-int<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:17.975Z|00050|rconn|WARN|br-int<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:17.975Z|00051|rconn|INFO|br-int<->tcp:127.0.0.1:6633: waiting 2 seconds before reconnect
2017-08-11T07:07:17.976Z|00052|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:17.979Z|00053|bridge|INFO|ovs-vswitchd (Open vSwitch) 2.6.1
2017-08-11T07:07:18.762Z|00054|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:18.762Z|00055|rconn|WARN|br-vlan<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:18.762Z|00056|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: waiting 2 seconds before reconnect
2017-08-11T07:07:18.762Z|00057|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:18.762Z|00058|rconn|WARN|br-ex<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:18.762Z|00059|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: waiting 2 seconds before reconnect
2017-08-11T07:07:19.762Z|00060|rconn|INFO|br-int<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:19.762Z|00061|rconn|WARN|br-int<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:19.762Z|00062|rconn|INFO|br-int<->tcp:127.0.0.1:6633: waiting 4 seconds before reconnect
2017-08-11T07:07:20.761Z|00063|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:20.762Z|00064|rconn|WARN|br-vlan<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:20.762Z|00065|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: waiting 4 seconds before reconnect
2017-08-11T07:07:20.762Z|00066|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:20.762Z|00067|rconn|WARN|br-ex<->tcp:127.0.0.1:6633: connection failed (Connection refused)
2017-08-11T07:07:20.762Z|00068|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: waiting 4 seconds before reconnect
2017-08-11T07:07:21.273Z|00069|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:21.379Z|00070|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:21.483Z|00071|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:21.588Z|00072|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:23.761Z|00073|rconn|INFO|br-int<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:23.762Z|00074|rconn|INFO|br-int<->tcp:127.0.0.1:6633: connected
2017-08-11T07:07:24.708Z|00075|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:24.761Z|00076|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:24.761Z|00077|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: connecting...
2017-08-11T07:07:24.762Z|00078|rconn|INFO|br-vlan<->tcp:127.0.0.1:6633: connected
2017-08-11T07:07:24.762Z|00079|rconn|INFO|br-ex<->tcp:127.0.0.1:6633: connected
2017-08-11T07:07:24.812Z|00080|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:24.916Z|00081|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:25.022Z|00082|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:25.136Z|00083|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:25.241Z|00084|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:25.346Z|00085|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:25.452Z|00086|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:25.574Z|00087|bridge|ERR|bridge br-int: mirror veth does not specify output; ignoring
2017-08-11T07:07:26.144Z|00088|connmgr|INFO|br-int<->unix: 1 flow_mods in the last 0 s (1 adds)
2017-08-11T07:07:26.150Z|00089|connmgr|INFO|br-int<->unix: 1 flow_mods in the last 0 s (1 adds)
2017-08-11T07:07:26.156Z|00090|connmgr|INFO|br-int<->unix: 1 flow_mods in the last 0 s (1 adds)
2017-08-11T07:07:26.162Z|00091|connmgr|INFO|br-int<->unix: 1 flow_mods in the last 0 s (1 adds)
2017-08-11T07:07:26.167Z|00092|connmgr|INFO|br-int<->unix: 1 flow_mods in the last 0 s (1 adds)
2017-08-11T07:07:27.669Z|00093|memory|INFO|219196 kB peak resident set size after 10.0 seconds
2017-08-11T07:07:27.669Z|00094|memory|INFO|handlers:17 ofconns:3 ports:12 revalidators:6 rules:26
2017-08-11T07:07:29.110Z|00095|connmgr|INFO|br-int<->unix: 110 flow_mods in the last 0 s (110 adds)
2017-08-11T07:07:34.694Z|00096|connmgr|INFO|br-int<->tcp:127.0.0.1:6633: 6 flow_mods in the 4 s starting 10 s ago (6 adds)
2017-08-11T07:07:35.127Z|00097|connmgr|INFO|br-vlan<->tcp:127.0.0.1:6633: 3 flow_mods in the 3 s starting 10 s ago (3 adds)
2017-08-11T07:07:35.557Z|00098|connmgr|INFO|br-ex<->tcp:127.0.0.1:6633: 2 flow_mods 10 s ago (2 adds)