I've also tested newer kernels and they're all susceptible to this (or a similar/related) problem. Sometimes I also see the following stack traces:

[  125.300088] BUG: unable to handle kernel NULL pointer dereference at 00000074
[  125.308050] IP: ma_put+0x25/0x40
[  125.308551] *pdpt = 000000001b027001 *pde = 0000000000000000 
[  125.309388] Oops: 0002 [#1] SMP
[  125.309885] Modules linked in: ufs msdos xfs openvswitch nsh nf_conntrack_ipv6 nf_nat_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_defrag_ipv6 nf_nat nf_conntrack isofs kvm_intel kvm joydev irqbypass input_leds serio_raw sch_fq_codel ib_iser rdma_cm iw_cm ib_cm ib_core iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear psmouse virtio_blk virtio_net floppy
[  125.316176] CPU: 0 PID: 1053 Comm: ovs-vswitchd Tainted: G        W        4.15.0-43-generic #46-Ubuntu
[  125.317585] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1ubuntu1 04/01/2014
[  125.318888] EIP: ma_put+0x25/0x40
[  125.319428] EFLAGS: 00010246 CPU: 0
[  125.319984] EAX: 00000000 EBX: db28ede0 ECX: 000000ff EDX: fffffe01
[  125.320873] ESI: dc692c00 EDI: dc692c6c EBP: db01fb20 ESP: db01fb1c
[  125.321765]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[  125.322531] CR0: 80050033 CR2: 00000074 CR3: 1b9cfac0 CR4: 000006f0
[  125.323471] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[  125.324405] DR6: fffe0ff0 DR7: 00000400
[  125.325018] Call Trace:
[  125.325447]  ipv6_mc_destroy_dev+0x4c/0x80
[  125.326103]  addrconf_ifdown+0x3c9/0x4c0
[  125.326746]  addrconf_notify+0x178/0x970
[  125.327390]  ? find_next_bit+0xa/0x10
[  125.327999]  ? cpumask_next+0x15/0x20
[  125.328607]  ? xfrm_policy_cache_flush+0x12f/0x14a
[  125.329364]  ? fib_add_ifaddr+0x170/0x170
[  125.330031]  ? inet6_ifinfo_notify+0xb0/0xb0
[  125.330718]  notifier_call_chain+0x51/0x80
[  125.331380]  raw_notifier_call_chain+0x11/0x20
[  125.332092]  call_netdevice_notifiers_info+0x25/0x50
[  125.332954]  rollback_registered_many+0x21f/0x390
[  125.333725]  unregister_netdevice_queue+0x74/0xe0
[  125.334451]  internal_dev_destroy+0x32/0x50 [openvswitch]
[  125.335210]  ovs_vport_del+0x39/0x40 [openvswitch]
[  125.335917]  __dp_destroy+0x90/0xc0 [openvswitch]
[  125.336649]  ovs_dp_cmd_del+0x71/0xd0 [openvswitch]
[  125.337406]  genl_rcv_msg+0x1fe/0x3a0
[  125.338074]  ? update_curr+0x80/0x240
[  125.338715]  ? genl_rcv+0x30/0x30
[  125.339257]  netlink_rcv_skb+0x6e/0xf0
[  125.339860]  genl_rcv+0x21/0x30
[  125.340377]  netlink_unicast+0x16f/0x200
[  125.341001]  netlink_sendmsg+0x247/0x390
[  125.341633]  ? netlink_unicast+0x200/0x200
[  125.342309]  sock_sendmsg+0x32/0x40
[  125.342892]  ___sys_sendmsg+0x249/0x260
[  125.343522]  ? default_wake_function+0x10/0x20
[  125.344236]  ? pollwake+0x68/0x90
[  125.344796]  ? wake_up_q+0x60/0x60
[  125.345368]  ? current_time+0x39/0x70
[  125.345983]  ? __wake_up_common_lock+0x82/0xb0
[  125.346697]  ? __atime_needs_update+0x7a/0x160
[  125.347407]  ? touch_atime+0x2b/0xb0
[  125.348002]  ? __wake_up_sync_key+0x1e/0x30
[  125.348682]  ? fsnotify_grab_connector+0x37/0x60
[  125.349421]  ? fsnotify_destroy_marks+0x10/0xa0
[  125.350145]  ? __fget_light+0x4d/0x60
[  125.350754]  __sys_sendmsg+0x3e/0x80
[  125.351351]  SyS_socketcall+0x185/0x680
[  125.351981]  ? mntput+0x20/0x40
[  125.352514]  ? __fput+0x15f/0x200
[  125.353082]  do_fast_syscall_32+0x7f/0x1e0
[  125.353754]  entry_SYSENTER_32+0x4e/0x7c
[  125.354401] EIP: 0xb7fd5d09
[  125.354892] EFLAGS: 00200293 CPU: 0
[  125.355477] EAX: ffffffda EBX: 00000010 ECX: bfb3b210 EDX: 00000000
[  125.356420] ESI: b7cf8000 EDI: bfb3b288 EBP: 00af8d00 ESP: bfb3b200
[  125.357367]  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b
[  125.358200] Code: ff ff ff 8d 76 00 3e 8d 74 26 00 55 89 e5 53 3e ff 48 4c 0f 88 48 04 05 00 74 0b 5b 5d c3 90 8d b4 26 00 00 00 00 89 c3 8b 40 10 <3e> ff 48 74 0f 88 31 04 05 00 75 05 e8 2a b6 01 00 89 d8 e8 53
[  125.360908] EIP: ma_put+0x25/0x40 SS:ESP: 0068:db01fb1c
[  125.361728] CR2: 0000000000000074
[  125.362329] ---[ end trace ce5d2e276f1f9782 ]---