Can clients create buffer lost?

I'm using an rpi4 router with a MacBook pro M2 connected to the router directly with a tplink ue300

Running speedtest.netperf from the router cli gives perfect latency results with sqm on and only drops 2 ms with it off.

But when I run the waveform speed test from the Mac I have to throttle Sqm download to 30% to get an A+. Upload is never a problem even at line rate.

I have an rt3200 dumb access point connected to the router too and running speedtest.netperf from there is also almost as good as from the rpi. But the Mac connecting WiFi at 1200Mbps phy speeds is even worse than when directly connected.

What might be causing the jitter when on the client?

Aggressive powersaving may, as could badly written drivers.

Any way to disable these for the tests?