Comment 12 for bug 1849479

Thx Marek for this data. I checked flows and I think that there are missing some flows in br-tun bridge before You restart neutron-ovs-agent.

For sure there is no flows:

table=0, priority=1,in_port="vxlan-ac100e47" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e46" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e49" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e39" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e2e" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e2b" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e42" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e29" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e2a" actions=resubmit(,4)
table=0, priority=1,in_port="vxlan-ac100e32" actions=resubmit(,4)

Which are responsible for packets comming to the host from vxlan tunnels. And next flow, which is:

table=0, priority=0 actions=drop

has got some packets in the counter.

Also there are missing flows like:

table=20, priority=2,dl_vlan=1,dl_dst=fa:16:3e:51:f4:84 actions=strip_vlan,load:0x79->NXM_NX_TUN_ID[],output:"vxlan-ac100e2b"
table=20, priority=2,dl_vlan=1,dl_dst=fa:16:3e:4b:f8:2d actions=strip_vlan,load:0x79->NXM_NX_TUN_ID[],output:"vxlan-ac100e29"

table=21, priority=1,arp,dl_vlan=1,arp_tpa=10.13.37.11 actions=load:0x2->NXM_OF_ARP_OP[],move:NXM_NX_ARP_SHA[]->NXM_NX_ARP_THA[],move:NXM_OF_ARP_SPA[]->NXM_OF_ARP_TPA[],load:0xfa163e51f484->NXM_NX_ARP_SHA[],load:0xa0d250b->NXM_OF_ARP_SPA[],move:NXM_OF_ETH_SRC[]->NXM_OF_ETH_DST[],mod_dl_src:fa:16:3e:51:f4:84,IN_PORT
table=21, priority=1,arp,dl_vlan=1,arp_tpa=10.13.37.10 actions=load:0x2->NXM_OF_ARP_OP[],move:NXM_NX_ARP_SHA[]->NXM_NX_ARP_THA[],move:NXM_OF_ARP_SPA[]->NXM_OF_ARP_TPA[],load:0xfa163e4bf82d->NXM_NX_ARP_SHA[],load:0xa0d250a->NXM_OF_ARP_SPA[],move:NXM_OF_ETH_SRC[]->NXM_OF_ETH_DST[],mod_dl_src:fa:16:3e:4b:f8:2d,IN_PORT

table=22, priority=1,dl_vlan=1 actions=strip_vlan,load:0x79->NXM_NX_TUN_ID[],output:"vxlan-ac100e47",output:"vxlan-ac100e46",output:"vxlan-ac100e49",output:"vxlan-ac100e39",output:"vxlan-ac100e2e",output:"vxlan-ac100e2b",output:"vxlan-ac100e42",output:"vxlan-ac100e29",output:"vxlan-ac100e2a",output:"vxlan-ac100e32"

So what I suspect here, it is some issue with l2population mechanism driver but I don't know exactly what the issue is there.

As a next steps, I think You should enable debug everywhere (on neutron-server and ovs-agents) and than try to reproduce the issue and check what is maybe missing or wrong there.
Also You can check if this dhcp requests are not going out from compute node to the vxlan tunnel, or maybe requests are sent properly and replies are dropped somewhere. It may also help us to understand exactly which missing flow is causing this problem.