Troubleshooting software flow offloading on Linksys EA6350v3

I have a gigabit fiber connection with DHCP. Without Software flow offloading and IRQbalance I am reaching around 580Mbps. As soon as I enable Software flow offloading, I am getting the full 940Mbps download, however I am noticing issues with twitch chat. At first I was getting random issues with other websites too, but after doing some digging I found that IPv6 is not working properly with software offloading, so I disabled it and the problems only show up on twitch now.
The problem I am facing is that about every 5 minutes twitch chat disconnects, and that only happens with software flow offloading. The issue occurs both on WiFi and Ethernet. When that happens I see the following message in the browser console: "The connection to wss:// was interrupted while the page was loading."
I tried contacting Twitch and they said the issue is on my end and I agree as it only manifests with this setting enabled.

OpenWrt version: 22.03.0-rc1 currently, but it was the same on 21.02.1

How would I go about troubleshooting this issue? Thank you!

ipq40xx simply isn't fast enough to route 1 GBit/s at wirespeed.

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@slh I saw that post before, I know I won't be able to do SQM at that speed. I am not running SQM at all. The problem I am facing is not dependent on the resources though. It's just small amount of ipv4 traffic that gets timed out every 5 minutes and I don't know why.

@anomeome That looks promising for the ipv6 problem, do you think it will resolve my issue as well?

Thank you!

Do you witness same issue with optimized build?

Yes, I just checked.

I wonder if it is maybe a hardware issue.

If you suspect a hardware issue, can you test with Linksys OEM firmware?

Only other suggestion is to review MTU on WAN port, but I don't think it will solve the issue.

I just changed the WAN MTU to 1420 and I think the problem is gone. This is really odd, I wasn't getting any fragmentation with the default 1500.
Should I also set LAN to match WAN MTU?
Also, how can I find the optimal MTU if the pind doesn't fragment until 1500?

Ask your ISP whether they have a recommended MTU value.

Someone else may be able to advise whether it is really necessary to edit the MTU on LAN interface. I'm not an expert, but I personally would Not change it.

fwiw, there has been reports when OpenWrt development snapshot first released for EA6350v3, with suspected MTU issues. See '3'.

I see, it makes sense now. I will do some trial and error until I get it right. Last time I contacted the ISP they weren't of much help so I am on my own. At least I know the cause and how to approach it. Thanks a lot!

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