Comment by InvaderFizz

That is likely because of AWDL and your WiFi card doing channel hopping to listen between packets.

Set your channels to 6/149/37 and the lag will probably vanish. Exactly because of this, I only run those channels, even across multiple APs.

In Europe, you may need to use 44 instead of 149.

There is currently no good way to keep AWDL off other than a script that just turns it off every 200ms, because of course Apple. Also, not always an option with work issued Macs.