LAN packets dropped every 30 seconds for 1-2 seconds

Hi guys.

I dont know when this problem started but I believe its not a long term problem as I would have noticed it sooner.

Basically every 30 seconds most traffic on my LAN stops responding for about a second or two, and this includes internet traffic.

Some info.

Two openwrt devices as switches, one of them is also wifi access point.
One pfsense device as firewall connected to first openwrt switch (which is also the WAP)

If I hold down a key in ssh, to anything whether its remote server, or a lan device including second openwrt switch and pfsense I get a sticky cursor for 1-2 seconds then it carries on.
If I do this on the main openwrt switch itself, which is what the ethernet from my PC is connected to as well as laptop via wifi, then it is fine.

Now I have also discovered the following.

If I disconnect the second openwrt switch from the first (pull out the cable), the issues stop. If I disconnect everything from that second switch and keep it connected, the issues do not stop.

Every 30 seconds there is a small spike of traffic on my main PC, the packet loss coincides with these traffic spikes, the spikes still occur when the second switch is disconnected, but there is no loss of traffic then. I have tried to diagnose whats going on here, as my laptop on windows doesnt have the same spikes, I reduced the size of the spikes disabling network discovery/upnp services, however the smaller spike remains and is from the kernel directly (system process).

Given the timings matching up I think the spikes might be related, and possible making the two openwrt's temporarily flood each other or something, so maybe it is multicast traffic I dont know.

The spikes stop when I put the PC in ipv6 only. However the laptop still gets the loss every 30 seconds to the second switch, also this happens still even when I disconnect my PC from the network, so the spikes are not the cause although incredibly coincidental they are the same timing.

This is one of the oddest and most frustrating network problems I have ever seen and would appreciate any advice.

Do you have a computer that is connected to the network by ethernet via a USB-C docking hub? If so, try removing the ethernet cable. Some docking hubs have a major firmware bug that will cause a broadcast storm when the computer goes to sleep or is disconnected.

If not, there are other things that could explain this, but I'm going on a hunch here for this first idea.

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Thank you for the reply, seems I got to the bottom of the problem, it doesnt make sense why it was killing my LAN, here is the information.

So the traffic on my PC was inbound traffic. Every 30 seconds.

I disconnected pfsense from the main switch, and the spikes stopped.

Connected it again and had a look and upnp was enabled from ages ago when I needed it to play UNO online, as soon as I disabled that the spikes stopped again.

Now with everything connected there is no LAN packet loss.

The spikes were only about 400kB/sec so its weird it killed my LAN on every spike.

Can internet traffic cause a broadcast storm?

I dont have a usb docking hub.