It's a CPU and chipset bug. AMD CPUs have built-in IO chipset that provides USB among other things. Most chipsets other than X570 use a different IO chip with different performance characteristics. The X570 chipset contains the same IO chip that the CPUs have so it's got the same characteristics. Depending the board some ports might be wired to the CPU others to the chipset. It's hard to know. The only certain combination is that a X570 boards have this issue. I don't know what USB chip is contained in the Threadripper boards. Either way, you use your board and if you notice USB dropouts when using high-bandwidth applications, get a PCIe controller for that. There's no other solution and there's no point spending time trying to workaround it. You can find many reports on the web. I was hit by this and tried even different boards till I finally gave up and got a add-in card. The AM5 platform seems to not suffer from this. I'm using the onboard USB controller on a X870 board at the moment. There's ptobably not much point of getting Intel just for this. I considered that and the performance per dollar was still much better on AMD even if having to buy a USB PCIe controller.