Hi here is a packet capture of an occurrence..
This packet capture is in the netns of the qrouter....

[root@overcloud-controller-1 ~]# ip netns ls
qdhcp-8897a5a6-dd5e-44d3-852f-c0dcd870b228
qdhcp-9b61e335-1b6c-498f-82b4-f660180e6876
qdhcp-ec0bad75-3466-43fb-b240-2b7d53a1d2c7
qdhcp-f76fcc81-0b57-4258-9e1a-04aa0c786428
qdhcp-b918b2ce-ef92-444d-80a0-9bf1f93406f3
qdhcp-3e184953-6df2-45c0-a0d4-7ca837110740
qdhcp-06c553c8-0adb-4b95-b2c4-4dc163f95a4f
qdhcp-184592ea-da08-4180-a9cb-a660125e5d1a
qrouter-b65e3bdc-390e-48b7-9cd9-fca429dafb45
[root@overcloud-controller-1 ~]# ip netns exec qrouter-b65e3bdc-390e-48b7-9cd9-fca429dafb45 ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
31: ha-bce4b526-c4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1446 qdisc noqueue state UNKNOWN qlen 1000
    link/ether fa:16:3e:2d:1c:2c brd ff:ff:ff:ff:ff:ff
    inet 169.254.192.2/18 brd 169.254.255.255 scope global ha-bce4b526-c4
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fe2d:1c2c/64 scope link 
       valid_lft forever preferred_lft forever
32: qr-1656d4d1-2c: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1446 qdisc noqueue state UNKNOWN qlen 1000
    link/ether fa:16:3e:54:77:0b brd ff:ff:ff:ff:ff:ff
33: qg-3f327e61-8b: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1496 qdisc noqueue state UNKNOWN qlen 1000
    link/ether fa:16:3e:a7:ae:63 brd ff:ff:ff:ff:ff:ff
[root@overcloud-controller-1 ~]# ip netns exec qrouter-b65e3bdc-390e-48b7-9cd9-fca429dafb45 bash
[root@overcloud-controller-1 ~]# tcpdump -nnvv -e -i qg-3f327e61-8b
tcpdump: WARNING: qg-3f327e61-8b: no IPv4 address assigned
tcpdump: listening on qg-3f327e61-8b, link-type EN10MB (Ethernet), capture size 65535 bytes
14:24:09.814889 08:81:f4:a6:dc:01 > 01:00:5e:00:00:01, ethertype IPv4 (0x0800), length 60: (tos 0xc0, ttl 1, id 30720, offset 0, flags [none], proto IGMP (2), length 32, options (RA))
    10.19.108.254 > 224.0.0.1: igmp query v2
14:24:13.799395 08:81:f4:a6:dc:01 > 33:33:00:00:00:0d, ethertype IPv6 (0x86dd), length 110: (class 0xc0, hlim 1, next-header PIM (103) payload length: 56) fe80:52:0:136c::fe > ff02::d: PIMv2, length 56
	Hello, cksum 0x018f (correct)
	  Hold Time Option (1), length 2, Value: 1m45s
	    0x0000:  0069
	  LAN Prune Delay Option (2), length 4, Value: 
	    T-bit=1, LAN delay 500ms, Override interval 2000ms
	    0x0000:  81f4 07d0
	  DR Priority Option (19), length 4, Value: 1
	    0x0000:  0000 0001
	  Address List Option (24), length 18, Value: 
	    2620:52:0:136c::fe
	    0x0000:  0200 2620 0052 0000 136c 0000 0000 0000
	    0x0010:  00fe
	  Generation ID Option (20), length 4, Value: 0x00ec032c
	    0x0000:  00ec 032c
14:24:21.481044 08:81:f4:a6:dc:01 > 33:33:00:00:00:01, ethertype IPv6 (0x86dd), length 86: (hlim 1, next-header Options (0) payload length: 32) fe80:52:0:136c::fe > ff02::1: HBH (rtalert: 0x0000) (padn) [icmp6 sum ok] ICMP6, multicast listener querymax resp delay: 10000 addr: ::
14:24:28.241400 fa:16:3e:ba:6f:6f > 33:33:ff:ba:6f:6f, ethertype IPv6 (0x86dd), length 86: (hlim 1, next-header Options (0) payload length: 32) fe80::f816:3eff:feba:6f6f > ff02::1:ffba:6f6f: HBH (rtalert: 0x0000) (padn) [icmp6 sum ok] ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ffba:6f6f
14:24:38.883558 08:81:f4:a6:dc:01 > 01:00:5e:00:00:0d, ethertype IPv4 (0x0800), length 68: (tos 0xc0, ttl 1, id 52817, offset 0, flags [none], proto PIM (103), length 54)
    10.19.108.254 > 224.0.0.13: PIMv2, length 34
	Hello, cksum 0x4fa8 (correct)
	  Hold Time Option (1), length 2, Value: 1m45s
	    0x0000:  0069
	  LAN Prune Delay Option (2), length 4, Value: 
	    T-bit=1, LAN delay 500ms, Override interval 2000ms
	    0x0000:  81f4 07d0
	  DR Priority Option (19), length 4, Value: 1
	    0x0000:  0000 0001
	  Generation ID Option (20), length 4, Value: 0x7c75897b
	    0x0000:  7c75 897b