Diagnosing / sniffing home network traffic

I have a 8800NL R2 as my main router and a R7800 connected to it in AP mode to provide increased wifi coverage. Everything is OK.

If I replace the 8000NL R2 with my BT SH2, the R7800 crashes/reboots on a random basis. When my laptop has been connected to the R7800 via wifi, I have seen a balloon pop-up in the Windows System Tray from the Netgear Net Genie - which says "High traffic" (or something similar). The alert is generated when the traffic reaches 20Mbps.

There's some people reporting random crashes. Any logs on the R7800 are cleared on reboot.

Is there an easy/cheapish way of monitoring the traffic between the SH2 and R7800 in order to determine what is happening?

Thanks

A cheap(ish) option is a managed switch.

https://amzn.to/3XlrMYi

You can then use port mirroring to mirror the traffic to another port and sniff the traffic with https://www.wireshark.org

Another option would be find someone who still has an old fashioned Ethernet hub rather than switch. Though that would limit you to 100mb and might well hide the problem.

It is also entirely possible that putting the managed switch between the two might make the problem vanish...

Thanks @andynormancx,

I've found a youtube video to explain the difference between an old fashioned ethernet hub and an ethernet switch.

I forgot to mention that I have a Netgear GS308v3 unmanaged switch in the mix. The 8800NL connects to the GS308v3 and that connects to the R7800 and other devices. The R7800 is only used for wireless devices. There is no wired connection apart from the GS308v3.

If I upgrade the GS308v3 to a GS308E (managed), although it is a little more expensive, I like Netgear, I should be able to mirror the port connected to the R7800 and consume with wireshark as suggested by you. Thank you.

It's really strange that the SH2 should cause the R7800 to crash.