Yours shows all the processing goes to the last core ie no irq balancing. May happen one bad day with more bandwidth too comlex sqm qdisc runs both ways on one core and drops occur...
nf_conntrack 1st field is what you count -> number of CT states (in hex)
dunno if 0021699a in softnet is RPS pushed to other CPU or software fragmentation 
root@Pupircha:~# tc -s qdisc
qdisc noqueue 0: dev lo root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc fq_codel 0: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
Sent 7780680125 bytes 6728777 pkt (dropped 0, overlimits 0 requeues 94)
backlog 0b 0p requeues 94
maxpacket 33308 drop_overlimit 0 new_flow_count 716 ecn_mark 0
new_flows_len 0 old_flows_len 0
qdisc cake 8009: dev eth1 root refcnt 2 bandwidth 512Mbit besteffort triple-isolate nonat nowash no-ack-filter split-gso rtt 100ms noatm overhead 44
Sent 2129306816 bytes 6677637 pkt (dropped 3, overlimits 2284474 requeues 0)
backlog 0b 0p requeues 0
memory used: 1591040b of 15140Kb
capacity estimate: 512Mbit
min/max network layer size: 26 / 1500
min/max overhead-adjusted size: 70 / 1544
average network hdr offset: 14
Tin 0
thresh 512Mbit
target 5ms
interval 100ms
pk_delay 38us
av_delay 8us
sp_delay 2us
backlog 0b
pkts 6677640
bytes 2129311302
way_inds 836762
way_miss 44125
way_cols 0
drops 3
marks 0
ack_drop 0
sp_flows 3
bk_flows 1
un_flows 0
max_len 67770
quantum 1514
qdisc ingress ffff: dev eth1 parent ffff:fff1 ----------------
Sent 7548668038 bytes 6699214 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev br-lan root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev docker0 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev br-7f0b91e0aac5 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev veth0ed15d2 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev veth4f15d29 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc cake 800a: dev ifb4eth1 root refcnt 2 bandwidth 512Mbit besteffort triple-isolate nonat wash no-ack-filter split-gso rtt 100ms noatm overhead 44
Sent 7764233240 bytes 6697146 pkt (dropped 2068, overlimits 2203080 requeues 0)
backlog 0b 0p requeues 0
memory used: 2695808b of 15140Kb
capacity estimate: 512Mbit
min/max network layer size: 46 / 1500
min/max overhead-adjusted size: 90 / 1544
average network hdr offset: 14
Tin 0
thresh 512Mbit
target 5ms
interval 100ms
pk_delay 18us
av_delay 7us
sp_delay 2us
backlog 0b
pkts 6699214
bytes 7767074110
way_inds 266212
way_miss 34441
way_cols 0
drops 2068
marks 0
ack_drop 0
sp_flows 3
bk_flows 1
un_flows 0
max_len 68064
quantum 1514
root@Pupircha:~# cat /proc/net/softnet_stat
005709b7 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 0032178c 00000000 00000000 00000000 00000000 00000000
00003dd9 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000001 00000000 00000000
009958f5 00000000 00000003 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000002 00000000 00000000
00002f4c 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000003 00000000 00000000
root@Pupircha:~# cat /proc/net/stat/nf_conntrack
entries clashres found new invalid ignore delete chainlength insert insert_failed drop early_drop icmp_error expect_new expect_create expect_delete search_restart
00000687 00000000 00000002 00000000 0000040b 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000002 00000000 00000000 00000000 00000000
00000687 00000000 00000000 00000000 0000003b 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000687 00000000 00000000 00000000 00001521 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000 00000000
00000687 00000000 00000000 00000000 00000022 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
root@Pupircha:~# tc -s qdisc
qdisc noqueue 0: dev lo root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc fq_codel 0: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
Sent 12504059478 bytes 10947944 pkt (dropped 0, overlimits 0 requeues 152)
backlog 0b 0p requeues 152
maxpacket 33308 drop_overlimit 0 new_flow_count 963 ecn_mark 0
new_flows_len 0 old_flows_len 0
qdisc cake 8009: dev eth1 root refcnt 2 bandwidth 512Mbit besteffort triple-isolate nonat nowash no-ack-filter split-gso rtt 100ms noatm overhead 44
Sent 2603048056 bytes 10368910 pkt (dropped 4, overlimits 2638327 requeues 1)
backlog 0b 0p requeues 1
memory used: 1591040b of 15140Kb
capacity estimate: 512Mbit
min/max network layer size: 26 / 1500
min/max overhead-adjusted size: 70 / 1544
average network hdr offset: 14
Tin 0
thresh 512Mbit
target 5ms
interval 100ms
pk_delay 268us
av_delay 60us
sp_delay 11us
backlog 0b
pkts 10368914
bytes 2603054008
way_inds 1437021
way_miss 50990
way_cols 9
drops 4
marks 0
ack_drop 0
sp_flows 8
bk_flows 1
un_flows 0
max_len 67770
quantum 1514
qdisc ingress ffff: dev eth1 parent ffff:fff1 ----------------
Sent 12158266111 bytes 10918306 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev br-lan root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev docker0 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev br-7f0b91e0aac5 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev veth0ed15d2 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc noqueue 0: dev veth4f15d29 root refcnt 2
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc cake 800a: dev ifb4eth1 root refcnt 2 bandwidth 512Mbit besteffort triple-isolate nonat wash no-ack-filter split-gso rtt 100ms noatm overhead 44
Sent 12488328215 bytes 10912468 pkt (dropped 5838, overlimits 2732923 requeues 0)
backlog 0b 0p requeues 0
memory used: 2695808b of 15140Kb
capacity estimate: 512Mbit
min/max network layer size: 46 / 1500
min/max overhead-adjusted size: 90 / 1544
average network hdr offset: 14
Tin 0
thresh 512Mbit
target 5ms
interval 100ms
pk_delay 17us
av_delay 4us
sp_delay 2us
backlog 0b
pkts 10918306
bytes 12495357127
way_inds 552967
way_miss 38129
way_cols 0
drops 5838
marks 1
ack_drop 0
sp_flows 8
bk_flows 1
un_flows 0
max_len 68130
quantum 1514
root@Pupircha:~# cat /proc/net/softnet_stat
0088bc0a 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 0048fe07 00000000 00000000 00000000 00000000 00000000
00004075 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000001 00000000 00000000
00fdc152 00000000 00000003 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000002 00000000 00000000
0000306c 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000003 00000000 00000000
root@Pupircha:~# cat /proc/net/stat/nf_conntrack
entries clashres found new invalid ignore delete chainlength insert insert_failed drop early_drop icmp_error expect_new expect_create expect_delete search_restart
00000a00 00000000 00000002 00000000 00000414 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000002 00000000 00000000 00000000 00000000
00000a00 00000000 00000000 00000000 0000003c 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000a00 00000000 00000000 00000000 00001554 00000000 00000000 00000000 00000000 00000000 00000000 00000000 0000003f 00000000 00000000 00000000 00000000
00000a00 00000000 00000000 00000000 00000026 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
root@Pupircha:~#
It worked fine on mikrotik stock FW. ISP doesn’t block torrents.
Total max conntctions 500
for 1 torrent 100
total slots 20
Max seed slots for torrent 4
10368910 pkt (dropped 4, overlimits 2638327 requeues 1)
1/4 of packets go dropped (overlimits == tail-drop) here. Just disable sqm. Torrents voluntarily tag themselves low priority.
I was going to double-check again at my workplace with a different ISP and... Anydesk server connection lost too at my home place.
So packets are lost not only to my VPN
Yeah, I know. There is no irqbalance installed by default on AX6s.
Probably you're right. I rebooted router today because I was making small MTU size (with DF and without) experiments a bit earlier.
The problem existed before installing SQM. Torrents work just fine. The connection to the VPN keeps dropping.
You can try steering vs irqbalance. Yours fine, no massive drops.
But it drops massively in and out. change qdisc to sfq or fq_codel.
This is the way it works on its default settings...
And now, thanks to my 10 minutes experiments with bittorrent, I'm in https://iknowwhatyoudownload.com statistics for violating copyright laws 
DAMN!!!
I double-checked it at work place, and suddenly it works. And I noticed that for some reason, uTorrent started working there. But at home, it's qBittorrent. I downloaded Transmission at home. And the problem went away!
I absolutely don't understand how this client can hack a router. But it can.
Thanks everyone for your help and support.
By the way, the QOS issue resolved itself. Transmission uses the entire bandwidth, but it doesn't jam other traffic.
Very unlikely but I will install it a bit later.
Bittorrents of course can jam other traffic but these days the issue not that severe as it was when uTP appeared. Nowadays they use low priority congestion control algorithm for that. It backs down quite effectively.
Thanks for the help anyway. It took me 2 months to dig into the problem. I bought a new industrial mini PC to use as a router. I have been fighting for 2 months with the technical support of both my Isp and the server side . And all this is because of the crooked torrent client.
If it is indeed the problem with OpenWrt it must be found... but I doubt that it is the case.
You'd be laughing but qbittorrent conciderably slows down my experience! I opened CNN website and it was loading like it's 1999. I used Appimage version.
EDIT: It's nothing critical, everything works fine but I can easily notice difference in loading typical websites. Video works just fine up to 4k.
I bet the problem that qbittorrent prefers TCP over UDP for downloading. At least this is what I see...
Most incoming connections are TCP (unlike Transmission) and, since they use in kernel congestion control like Cubic, they effectively compete with your other typical Internet connections just throttling them down by number. And, to make it worse, you had only one SQM bin...
But, unlike Transmission, qbittorrent correctly marks outgoing traffic as lower priority, so it gets to Bulk if you have correctly functioning SQM with several bins.
EDIT: I tried another, much lower end, PC in my LAN and it worked just fine. So SQM works as intended, no considerable drop in experience. IMO the problem is in preference of TCP over UDP, 100 connections can effectively throttle others coming to or from same PC.
P.S. don't blame me, I didn't even try to configure qbittorrent. I bet it can be fixed. I tested default settings over not so default setting of my OpenWrt router.
I’m on Windows 11 Pro 25H2 26200.7171 and it was killing my surfing totally. I won't tell you the qBittorrent version - I've already deleted it completely.
It doesn't matter. The problem is in preference of TCP over UDP (uTP). Transmission uses UDP (uTP) whenever possible. And uTP, even if SQM/AQM doesn't exist, will always back down in presence of TCP connections managed almost universally by Cubic (including Windows).
EDIT: https://en.wikipedia.org/wiki/LEDBAT - this is what is used by uTP (essentially UDP + LEDBAT to manage network throughput).
You're too hasty. You can tune qbittorrent up. I checked it and it works (see advanced settings in very bottom). The problem was not in OpenWrt but in default settings of your Bittorrent client which allowed easy saturation of the connection between you and your router.
