Flapping igc device in promiscuos mode when running pppoe over vlan at 940Mbps

[sja1440]

I have a reproducible problem which occurs when downloading at my ISP's maximal rate (940 Mbps effective). My ISP requires me to access his systems using pppoe over a vlan.

When I enable promiscuous mode on the underlying igc device, I see kernel logs showing the  igc device going down and then coming up again a few seconds later. The pppoe logs show no entries for this event. The user experience is that of a stutter.

After disabling  promiscuous mode the problem no longer occurs.

I am able to produce the problem with speedtest.net using a fresh OPNsense 23.7.8-amd64 install on the VP4670 configured only with:
* powerd
* tunables net.isr.dispatch=deferred and net.isr.maxthreads=6 (I have disabled multithreading)
* WAN interface to be pppoe over vlan over an i225V NIC.
* promiscuous mode set on the igc device

My hardware is a Protectli VP4670 with Intel I225-V Rev. B3 2.5G ethernet nics.

Is this a known issue? 

Is there a way to avoid the problem when using promiscuous mode?

[sja1440]

In the end I realised that infact the tunables net.isr.dispatch=deferred and net.isr.maxthreads=6 had not being set.

After setting them, the problem went away.