'Thanks, I will try and check this out,
Not sure if this could provide more info.
I quickly did a tcpdump, see below.
openwrt to internal lan device
13:24:28.856775 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911448014 ecr 0,nop,wscale 6], length 0
13:24:28.857094 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810848594 ecr 911448014,nop,wscale 7], length 0
13:24:29.859735 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911449017 ecr 0,nop,wscale 6], length 0
13:24:29.859930 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810849597 ecr 911448014,nop,wscale 7], length 0
13:24:30.885635 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810850623 ecr 911448014,nop,wscale 7], length 0
13:24:31.939756 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911451097 ecr 0,nop,wscale 6], length 0
13:24:31.939989 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810851677 ecr 911448014,nop,wscale 7], length 0
13:24:33.957616 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810853695 ecr 911448014,nop,wscale 7], length 0
13:24:36.020314 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911455177 ecr 0,nop,wscale 6], length 0
13:24:36.020467 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810855757 ecr 911448014,nop,wscale 7], length 0
13:24:40.101614 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810859839 ecr 911448014,nop,wscale 7], length 0
13:24:44.499711 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911463657 ecr 0,nop,wscale 6], length 0
13:24:44.499876 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810864237 ecr 911448014,nop,wscale 7], length 0
13:24:52.645603 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810872383 ecr 911448014,nop,wscale 7], length 0
13:25:01.139648 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911480297 ecr 0,nop,wscale 6], length 0
13:25:01.139781 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810880877 ecr 911448014,nop,wscale 7], length 0
13:25:17.221559 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810896959 ecr 911448014,nop,wscale 7], length 0
13:25:33.779814 eth0 In IP 10.192.1.1.41884 > 10.192.0.5.22: Flags [S], seq 15711014, win 64240, options [mss 1460,sackOK,TS val 911512937 ecr 0,nop,wscale 6], length 0
13:25:33.780034 eth0 Out IP 10.192.0.5.22 > 10.192.1.1.41884: Flags [S.], seq 2923662851, ack 15711015, win 65160, options [mss 1460,sackOK,TS val 3810913517 ecr 911448014,nop,wscale 7], length 0
internal lan to openwrt
13:29:03.544838 IP 10.192.0.5.42360 > 10.192.1.1.22: Flags [S], seq 466049534, win 64240, options [mss 1460,sackOK,TS val 3811123274 ecr 0,nop,wscale 7], length 0
13:29:03.544838 IP 10.192.0.5.42360 > 10.192.1.1.22: Flags [S], seq 466049534, win 64240, options [mss 1460,sackOK,TS val 3811123274 ecr 0,nop,wscale 7], length 0
13:29:03.545299 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911722694 ecr 3811123274,nop,wscale 6], length 0
13:29:03.545347 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911722694 ecr 3811123274,nop,wscale 6], length 0
13:29:04.587484 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911723737 ecr 3811123274,nop,wscale 6], length 0
13:29:04.587549 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911723737 ecr 3811123274,nop,wscale 6], length 0
13:29:06.667479 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911725817 ecr 3811123274,nop,wscale 6], length 0
13:29:06.667546 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911725817 ecr 3811123274,nop,wscale 6], length 0
13:29:10.747513 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911729897 ecr 3811123274,nop,wscale 6], length 0
13:29:10.747577 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911729897 ecr 3811123274,nop,wscale 6], length 0
13:29:19.067479 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911738217 ecr 3811123274,nop,wscale 6], length 0
13:29:19.067545 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911738217 ecr 3811123274,nop,wscale 6], length 0
13:29:35.707477 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911754857 ecr 3811123274,nop,wscale 6], length 0
13:29:35.707584 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [S.], seq 1652489149, ack 466049535, win 65160, options [mss 1460,sackOK,TS val 911754857 ecr 3811123274,nop,wscale 6], length 0
13:32:37.294518 IP 10.192.0.5.42360 > 10.192.1.1.22: Flags [P.], seq 1:41, ack 1, win 502, options [nop,nop,TS val 3811337023 ecr 911722694], length 40
13:32:37.294518 IP 10.192.0.5.42360 > 10.192.1.1.22: Flags [P.], seq 1:41, ack 1, win 502, options [nop,nop,TS val 3811337023 ecr 911722694], length 40
13:32:37.294920 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [R], seq 1652489150, win 0, length 0
13:32:37.294971 IP 10.192.1.1.22 > 10.192.0.5.42360: Flags [R], seq 1652489150, win 0, length 0`