Hi, guys,
Just a heads-up, this has already been reported here. It's quite unexpected for a stable LTS kernel, though.
[ 32.053822] invalid inflight: 1 state 1 cwnd 10 mss 1448
[ 32.059358] ------------[ cut here ]------------
[ 32.064209] WARNING: CPU: 2 PID: 6244 at 0xffffffff8166702d
[ 32.069998] Modules linked in: nf_nat_pptp nf_conntrack_pptp nf_conntrack_ipv6 lzo lz4 iptable_nat ipt_REJECT ipt_MASQUERADE xt_time xt_tcpudp xt_tcpmss xt_statistic xt_state xt_recent xt_nat xt_multiport xt_mark xt_mac xt_limit xt_length xt_hl xt_helper xt_ecn xt_dscp xt_conntrack xt_connmark xt_connlimit xt_connbytes xt_comment xt_TCPMSS xt_REDIRECT xt_LOG xt_HL xt_FLOWOFFLOAD xt_DSCP xt_CT xt_CLASSIFY wireguard ts_fsm ts_bm nf_reject_ipv4 nf_nat_tftp nf_nat_snmp_basic nf_nat_sip nf_nat_redirect nf_nat_proto_gre nf_nat_masquerade_ipv4 nf_nat_irc nf_conntrack_ipv4 nf_nat_ipv4 nf_nat_h323 nf_nat_ftp nf_nat_amanda nf_nat nf_log_ipv4 nf_flow_table_hw nf_flow_table nf_defrag_ipv6 nf_defrag_ipv4 nf_conntrack_tftp nf_conntrack_snmp nf_conntrack_sip nf_conntrack_rtcache nf_conntrack_proto_gre nf_conntrack_netlink
[ 32.144411] nf_conntrack_irc nf_conntrack_h323 nf_conntrack_ftp nf_conntrack_broadcast ts_kmp nf_conntrack_amanda lzo_decompress lzo_compress lz4_decompress lz4_compress iptable_raw iptable_mangle iptable_filter ipt_ECN ip6table_raw ip_tables sch_cake nf_conntrack sch_tbf sch_ingress sch_htb sch_hfsc em_u32 cls_u32 cls_tcindex cls_route cls_matchall cls_fw cls_flow cls_basic act_skbedit act_mirred i2c_dev ledtrig_heartbeat xt_set ip_set_list_set ip_set_hash_netportnet ip_set_hash_netport ip_set_hash_netnet ip_set_hash_netiface ip_set_hash_net ip_set_hash_mac ip_set_hash_ipportnet ip_set_hash_ipportip ip_set_hash_ipport ip_set_hash_ipmark ip_set_hash_ip ip_set_bitmap_port ip_set_bitmap_ipmac ip_set_bitmap_ip ip_set nfnetlink nf_log_ipv6 nf_log_common ip6table_mangle ip6table_filter ip6_tables ip6t_REJECT
[ 32.218615] x_tables nf_reject_ipv6 igb ifb ip6_udp_tunnel udp_tunnel zram zsmalloc sha256_ssse3 sha1_ssse3 ccp_crypto rsa_generic mpi asn1_decoder akcipher ccp sha256_generic sha1_generic authenc crypto_acompress sdhci_pltfm leds_apu2 ptp pps_core
[ 32.242016] CPU: 2 PID: 6244 Comm: awk Not tainted 4.14.144 #0
[ 32.248161] Hardware name: PC Engines APU2/APU2, BIOS 4.0.7 02/28/2017
[ 32.255027] task: ffff888115e9ae00 task.stack: ffffc90005674000
[ 32.261223] RIP: 0010:0xffffffff8166702d
[ 32.265293] RSP: 0000:ffff88811ed03e70 EFLAGS: 00010282
[ 32.270764] RAX: 000000000000002c RBX: ffff888117af9f00 RCX: 0000000000000000
[ 32.278251] RDX: ffff88811ed1ba60 RSI: ffff88811ed16358 RDI: ffff88811ed16358
[ 32.285665] RBP: ffff88811ed03e88 R08: 0000000000000000 R09: 00000000000001fb
[ 32.293137] R10: ffff88811ed03e68 R11: 0000000000000000 R12: ffff888117afa050
[ 32.300804] R13: ffff888117afa050 R14: ffff88811ed03ef0 R15: ffff88811ed1a4a8
[ 32.308364] FS: 00007fb91e49bd68(0000) GS:ffff88811ed00000(0000) knlGS:0000000000000000
[ 32.316890] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 32.322971] CR2: 00007f29cffdb3d8 CR3: 0000000115158000 CR4: 00000000000406e0
[ 32.330468] Call Trace:
[ 32.333056] <IRQ>
[ 32.335150] 0xffffffff81668cf5
[ 32.338511] 0xffffffff81668e9b
[ 32.341889] ? 0xffffffff81668e70
[ 32.345410] 0xffffffff810ca69f
[ 32.348905] 0xffffffff810ca834
[ 32.352292] ? 0xffffffff81040d3e
[ 32.355790] ? 0xffffffff810d5d60
[ 32.359336] 0xffffffff81a000ba
[ 32.362606] 0xffffffff81087e52
[ 32.365974] 0xffffffff818024d7
[ 32.369232] 0xffffffff81801aec
[ 32.372522] </IRQ>
[ 32.374674] RIP: 0033:0x419f71
[ 32.377898] RSP: 002b:00007ffdeea9dd40 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff10
[ 32.385842] RAX: 00000000007d3430 RBX: 00000000007d3446 RCX: 00000000007d33a6
[ 32.393293] RDX: 00000000007d33a5 RSI: 00000000007d3460 RDI: 00000000007d3440
[ 32.400728] RBP: 00007fb91e49c470 R08: 8080808080808080 R09: fefefefefefefeff
[ 32.408293] R10: 00000000007d0c20 R11: 00000000007d1060 R12: 0000000000000001
[ 32.415851] R13: 00007fb91e49c668 R14: 0000000000000000 R15: 00000000007cf280
[ 32.423443] Code: 74 2b 80 3d e6 c1 81 00 00 75 22 0f b6 53 12 8b 8b 14 06 00 00 41 89 c0 48 c7 c7 b0 03 d4 81 c6 05 c9 c1 81 00 01 e8 ef 30 a5 ff <0f> 0b c6 83 62 04 00 00 00 e9 ce 00 00 00 8b 93 98 05 00 00 85
[ 32.443517] ---[ end trace 9ec181c9672e3c3a ]---