Nighthawk RAX50: slow 2.4Ghz for Wifi 6 clients when device plugged into USB port

Per subject, for any Wifi 6 clients (Samsung Galaxy S20, AX1650 on laptop) at distance from the router (and hence on the 2.4 Ghz band), WiFi speeds are terrible (~5 mbps connection) when HDD plugged into the USB port.  Wifi 5 clients right next to the Wifi 6 clients achieve 60 mbps plus.  

Removing the USB devices resolves the issue with all devices connecting at the same approx. speed.  The 5Ghz band seems unaffected.

I can see same issue posted for RAX120 here: https://community.netgear.com/t5/Nighthawk-Routers-with-WiFi-6-AX/Horrible-2-4GHz-Speed/td-p/1840176.

Is this a fundamental design flaw for the RAX series routers, or is there a resolution?  Tried changing many settings on router, but none have impact (even turning off AX wifi....the Wifi 6 clients still connect at the same v. low speeds vs. Wifi 5 clients on the 2.4Ghz band....so not sure exactly what is going on).